LABORATORY DIAGNOSTICS OF THE KIDNEY DISEASES
The kidneys are paired organs, which are responsible for the constancy of
the internal environment in the organism and elimination of the metabolism end-products.The
kidneys regulate water-electrolyte balance, acid-base balance, excretion of
metabolic wastes, osmotic pressure. Besides, they take part in the regulation
of blood pressure and R.B.C production.
1.
Structure and function of the kidneys
Each kidney is composed of 2 layers: the cortex or
outer layer is brownish- red and the medulla or inner layer is lighter in
colour. The nephron is the functioning unit of the kidney. Each kidney contains
more than a million of nephrons.
It consists of renal corpuscle, which contains
glomerulus surrounded by hollow capsule (Bowman’s capsule). Besides each
nephron contains: proximal convoluted tubules, a descending limb of the loop of
Henle, collecting tubules and distal convoluted tubules.
The 2 principal types of nephron are classified
according to their position in the kidneys:
1. Cortical nephrons (85%), which are situated in the
cortex.
2. Yuxtamedullary nephrons (15%)
The kidneys are the most important organs of excretion.
A human dies when the kidneys are not functioning for 4-6 days.
A.
Renal hormones
In addition to their
involvement in excretion and metabolism, the kidneys also have endocrine
functions. They produce the hormones erythropoietin and calcitriol and
play a decisive part in producing the hormone angiotensin II by
releasing the enzyme renin. Renal prostaglandins have a local effect on
Na+ resorption.
Calcitriol (vitamin
D hormone, 1α,25-dihydroxycholecalciferol) is a
hormone closely related to the steroids that is involved in Ca2+
homeostasis. In the kidney, it
is formed fromcalcidiol by hydroxylation at C-1.
The activity of calcidiol-1-monooxygenase
[1] is enhanced by the hormone parathyrin (PTH).
Erythropoietin
is a peptide hormone that is formed predominantly by
the kidneys, but also by the liver. Together with other factors known as “colony-stimulating
factors” (CSF), it regulates the differentiation of stemcells in the bone
marrow.
Erythropoietin release is
stimulated by hypoxia (low pO2). Within hours, the hormone ensures
that erythrocyte precursor cells in the bone marrow are converted to
erythrocytes, so that their numbers in the blood increase.
Renal damage leads to reduced
erythropoietin release, which in turn results in anemia. Forms of anemia
with renal causes can now be successfully treated using erythropoietin produced
by genetic engineering techniques.
The hormone is also
administered to dialysis patients. Among athletes and sports professionals,
there have been repeated cases of erythropoietin being misused for doping
purposes.
Renin–angiotensin
system
The peptide hormone
angiotensin II is not synthesized in a hormonal gland, but in the blood. The
kidneys take part in this process by releasing the enzyme renin.
Renin [2]
is an aspartate proteinase. It is formed by the kidneys as a precursor
(prorenin), which is
proteolytically activated into renin and released into the
blood. In the blood plasma,
renin acts on angiotensinogen, a plasma glycoprotein in the α2-globulin
group, which like almost all plasma proteins is synthesized in the liver. The
decapeptide cleaved off by renin is called angiotensin I. Further
cleavage by peptidyl dipeptidase A (angiotensin-converting enzyme,
ACE), a membrane enzyme located on the vascular endothelium in the lungs
and other tissues, gives rise to the octapeptide angiotensin II [3],
which acts as
a hormone and
neurotransmitter. The lifespan of angiotensin II in the plasma is only a few
minutes, as it is rapidly broken down by other peptidases (angiotensinases
[4]), which occur in many different tissues.
The plasma level of
angiotensin II is mainly determined by the rate at which renin is released by
the kidneys. Renin is synthesized by juxtaglomerular cells, which release it
when sodium levels decline or there is a fall in blood pressure.
Effects
of angiotensin II.
Angiotensin II has neffects on
the kidneys, brain stem, pituitary gland, adrenal cortex, blood vessel walls,
and heart via membrane-located receptors. It increases
blood pressure by triggering vasoconstriction
(narrowing of the blood vessels). In
the kidneys, it promotes the retention
of Na+ and water and reduces potassium secretion. In the brain stem
and at nerve endings in the sympathetic nervous system, the effects of
angiotensin II lead to increased tonicity (neurotransmitter
effect). In addition, it
triggers the sensation of thirst. In the pituitary gland,
angiotensin II stimulates vasopressin
release (antidiuretic hormone) and corticotropin (ACTH) release. In
the adrenal cortex, it increases the biosynthesis and release of
aldosterone, which promotes sodium and water
retention in the kidneys. All
of the effects of angiotensin II lead directly or indirectly to increased
blood pressure, as well as increased sodium and water retention. This
important hormonal system for blood pressure regulation
can be pharmacologically
influenced by inhibitors at various points:
• Using angiotensinogen
analogs that inhibit renin.
• Using angiotensin I analogs
that competitively inhibit the enzyme ACE [3].
• Using hormone antagonists
that block the binding of angiotensin II to its receptors.
Mechanism of the urine formation
How urine is formed?
There are 3 basic renal processes: filtration,
reabsorption and secretion. Glomerular filtration is caused by difference
between glomerular pressure (
The effective filtration pressure is approximately
70mmHg -(30mmHg + 20mmHg) =20mmHg . Oncotic + capsular pressure must be lower
than glomerular pressure. As a result of
the filtration primary urine is formed. Assuming that the kidneys are healthy
and filter approximately 20% of the plasma they receive each minute, they will
produce 180 to
Some of the blood that passes through the kidneys,
in the other words, is “cleared” from waste products.
If a substance is neither reabsorbed nor secreted by
the tubules, the amount of excreted per minute in the urine will be equal to
the amount that is filtered out of the glomeruli.
The renal plasma clearence is the volume of plasma
from which a substance is completely removed in 1 minute by excretion in the
urine.
Renal plasma clearence is calculated using formula:
C = V*U
P
Where C-clearence
V-urine formation volume per minute (ml per min)
U-concentration of substance in urine (mg%)
P-concentration of substance in plasma (mg%)
For example: clearence of inulin, creatinine is
equal to 125 ml per min (because they are not being reabsorbed); These substances are used for the
determination of renal plasma clearence in medicine.
If clearence >125, it means that substance
is intensively secreted in tubules.
If clearence <125, it means that there is
some inflammatory process of the kidneys (nephritis), which caused azotemia.
Tests of glomerular function
The GFR depends on the net pressure across the glomerular membrane, the physical nature of the membrane and its surface area, which in turn reflects the number of functioning glomeruli. All
three factors may be modified by
disease, but in the absence of
large changes in filtration pressure or in the structure of the glomerular membrane, the GFR provides a useful index of the numbers of functioning glomeruli. It gives an estimate of
the degree of renal
impairment by disease.
Accurate measurement of
the GFR by clearance tests requires determination
of the concentrations, in plasma and
urine, of a substance that is filtered
at the glomerulus, but which is neither reabsorbed nor secreted by the
tubules; its concentration in plasma needs
to remain constant throughout the
period of urine collection. It is convenient if the substance is present
endoge-nously, and important for it to
be readily measured. Its clearance
is given by
Clearance = U- V/P
where
U is the concentration in urine, V is the volume of urine produced per minute and P is
the concentration in plasma. When
performing this calculation
manually, care should be taken to ensure
consistency of units, especially for the plasma and urine concentrations.
Inulin
(a complex plant carbohydrate) meets these criteria, apart from the fact that it is not an endogenous compound, but needs to be administered by IV infusion. This makes it completely impractical for routine clinical use, but it
remains the original standard against which other
measures of GFR are assessed.
Measurement of creatinine
clearance
Creatine
is synthesised in the liver, kidneys and pancreas,
and is transported to its sites of usage, principally
muscle and brain. About 1-2% of the
total muscle creatine pool is converted daily to creatinine through the spontaneous, non-enzymatic loss of
water. Creatinine is an end product of nitrogen metabolism, and as such
undergoes no further metabolism, but is
excreted in the urine. Creatinine
production reflects the body's total muscle mass.
Creatinine
meets some of the criteria mentioned above. Creatinine
in the plasma is filtered freely at the
glomerulus, but its concentration may not remain constant over the period of urine collection. A small amount of this filtered creatinine
undergoes tubular reabsorption. A larger amount, up to 10% of urinary creatinine, is actively secreted into the urine by the tubules. Its measurement in plasma is subject to analytical overestimation. In
practice, the effects of tubular secretion and analytical overestimation tend to cancel each other out at normal levels of GFR, and the creatinine clearance is a fair approximation to the GFR. As
the GFR falls, however, creatinine clearance progressively overestimates the true GFR.
Creatinine
clearance is usually about 110 mL/min in the 20-40-year-old
age group. Thereafter, it falls slowly but
progressively to about 70 mL/min in
people over
Creatinine clearance or plasma [creatinine]?
Measurement
of plasma [creatinine] is more precise than creatinine clearance, as there are two extra sources of imprecision in clearance measurements, that is, timed measurement of urine volume and urine [creatinine]. Accuracy of urine collections
is very dependent on patients'
cooperation and the care with which
the procedure has been explained or
supervised. The combination of these errors causes an imprecision (1 SD) in the creatinine clearance of about 10% under ideal conditions with 'good' collectors; this increases to 20-30% under less ideal conditions. This means that large
changes in creatinine clearance may
not reflect any real change in renal
function.
It will be
apparent that creatinine clearance measurements are potentially unreliable.
Although creatinine clearance measurements
are commonly made, accurate measurement of GFR is not often required. Indications for its measurement include
determining the dose of a number of potentially toxic drugs that are
cleared from the body by renal excretion,
investigation of patients with minor abnormalities
of renal function and assessment of possible kidney donors.
In
most circumstances, however, assessment of glomerular function can be made and changes in GFR over time can be monitored, biochemically, by measurement of plasma [creatininej rather than by measurement of creatinine clearance, because
1 plasma
[creatinine] normally remains
fairly constant throughout
adult life, whereas creatinine clearance
declines with advancing age;
2 plasma [creatinine] correlates as well with GFR as does creatinine clearance in patients with
renal disease;
3 measurements
of plasma [creatinine] are
as effective in detecting early renal disease as creati nine clearance, despite the form of the relation
ship described above, because of
the imprecision in measuring
creatinine clearance;
4 sequential plasma [creatinine]
measurements enable the progress of renal disease
to be followed with better precision than
creatinine clearance.
Low plasma [creatinine]
A low [creatinine] is found in subjects with a small total muscle mass (Table 4.1). A low plasma
[creatinine] may therefore
be found in children, and values
are, on average, normally lower in women than
in men. Abnormally low values may be found in
wasting diseases and starvation, and in patients treated with corticosteroids, due to their protein catabolic effect.
Creatinine synthesis is increased in
pregnancy, but this is more than offset by the ncombined effects of the retention of fluid and
the physiological rise in GFR that occur in
pregnancy, so plasma [creatinine] is usually low.
High plasma [creatinine]
Plasma
[creatinine] tends to be higher in subjects with a large muscle mass (Table 4.1). Other non-renal causes of increased plasma [creatinine] include the following:
1
A
high meat intake can cause a temporary increase.
2
Transient,
small increases may occur after vigor ous exercise.
3
Some
analytical methods are not specific for creatinine. For example, plasma [creatinine] will be overestimated by some methods in the presence of high concentrations of acetoacetate or cephalosporin antibiotics.
4
Some
drugs (e.g. salicylates, cimetidine) compete with creatinine
for its tubular
transport mechanism,
thereby reducing tubular secretion of
creatinine and elevating plasma [creatinine].
If
non-renal causes can be excluded, an increased plasma [creatinine] indicates a fall in GFR. The renal causes of this include:
1
any disease in which
there is impaired renal perfusion (e.g.
reduced blood pressure, fluid depletion, renal artery stenosis);
2
most
diseases in which there is loss of functioning
nephrons (e.g. acute
and chronic glomerulonephritis);
3
diseases
where pressure is increased on the tubular side of the nephron (e.g. urinary
tract obstruction due to
prostatic enlargement).
Other tests of glomerular
function
Isotope tests
A number of isotopic markers (e.g. 51Cr-EDTA, 99Tc-DTPA) are almost entirely cleared from the circulation by glomerular filtration. They are injected or infused, and the measurement of their
disappearance from the circulation or appearance in urine can be used to calculate the GFR. These tests
have largely superceded the use of inulin clearance, but are not widely used in routine clinical practice.
ß2-microglobulin
ß2-microglobulin is a small (11.8 kDa) protein
found on the cell surface of all nucleated cells, as part of the class 1 major histocompatibility complex. It is shed into the blood, where it is
normally present in low concentrations. Its small
size allows it to pass freely through the glomerular membrane, following which it is reabsorbed and catabolised in the proximal tubules. As glomerular filtration falls,
the concentration of ß2-microglobulin
rises, making it a good indicator of GFR in
normal people, since it is not affected by muscle mass or diet. However, its concentration also increases in a number of malignancies and inflammatory conditions. The prognosis in multiple myeloma is adversely influenced by increasing tumour mass and by declining renal function, both of which cause ß2-microglobulin to rise, making it a helpful prognostic indicator in this condition.
Cystatin
C
Cystatin
C is a cysteine protease inhibitor produced by all nucleated cells. It is a small (13 kDa) basic protein which is freely filtered by the
glomerulus and almost completely
reabsorbed and catabolised by the proximal tubules.
Serum levels of cystatin C are
independent of weight, height, muscle mass, age (over 1 year) or sex, and it has a stable production rate. Serum levels correlate well with GFR,
performing at least as well as
creatinine, and being less subject to
confounding influences. However, at present its measurement is much more
expensive and not as rapid as the measurement of creatinine, so despite
promise as a measurement, it is unlikely to
be widely adopted in the near future.
2.
Mechanisms of reabsorption in
kidneys’ tubules.
The biggest part of primary urine during its
transference through kidney tubules (the length of all kidney tubules is more
than 100km) return many components into blood. Approximately all important for
organism substances are reabsorbed. The mechanisms involved in this process may
be divided into 2 categories : simple diffusion and active transport.
The main portion of substances is reabsorbed by
active transport which requires the use
of metabolic energy. That’s why system of active transport is very
developed in kidneys tubules. High activity of Na+/K+
ATPase creates Na+/K+ gradient for secondary active
transport of different substances. All the substances are divided into 3 groups
due to their extent of reabsorption in proximal tubules :
1.Substances which are actively reabsorbed
2.Substances which are reabsorbed not enough
3.Substances which are not reabsorbed
Ions of sodium, chloride, magnesium, calcium, water,
glucose and other monosaccharides, amino acids, phosphates, hydrocarbonates,
proteins, etc are actively reabsorbed.
Glucose and proteins are reabsorbed approximately
all, amino acids - up to 93%, water – up
to 96%, NaCl- up to 70%, the other substances- more than 50%. Reabsorption of
Na ions by the tubular epithelial cells is generally regarded as an
active transport. Firstly Na ions pass from the kidney tubules into the
epithelial cells and from there- into extracellular space.
Tubular reabsorption of Cl and HCO3-
occurs passively in association with reabsorption of Na+.
Water is absorbed isoosmotically with Na and also by flowing along the osmotic
gradient due to increase of osmotic pressure in extracellular space. From there
substances pass into capillaries.
Glucose and amino acids are transported by the
special mediators in association with Na. They use energy of Na+ -
gradient on membrane Ca and Mg are reabsorbed by the help of special ATPase.
Protein is reabsorbed by endocytosis.
Urea and uric acid belong to substances which are
being reabsorbed not enough. They are transported by simple diffusion into
extracellular space, and from there-in loop of Henle.
Creatinine, mannitol, inulin - are substances which
are not being reabsorbed.
Functional significance of different parts of kidney
tubules in the urine formation is heterogeneous. Descending and ascending limbs
of the loop of Henle form the countercurrent system which takes part in
concentration and dilutation of the urine due to the normal range for the
specific gravity of urine which is from 1.002 to 1.030.
Liquid, which is transferred from the proximal
tubule to descending limb of the loop of Henle, passes in kidney zone where
concentration of osmoactive substances is higher, than in cortex. The walls of
the ascending limb of the loop of Henle are not permeable to water. Salt (NaCl)
is extruted into the surrounding tissue fluid. The descending limb does not
actively transport salt. It is however, permeable to water.
Since the surrounding interstitial fluid is
hypertonic to the filtrate in the descending
limb, water is drawn out of the descending limb by osmosis and enters
blood capillaries. This system results in a gradually increasing concentration
of renal tissue fluid from the cortex to the inner medulla; the osmolality of
tissue fluid increases from 300mOsm/l to 1450mOsm/l.
Tests of tubular function
Specific disorders affecting the renal tubules may affect the ability to
concentrate urine or to excrete an
appropriately acidic urine, or may cause impaired reabsorption of amino acids, or glucose, or phosphate, etc. In some conditions, these defects occur singly; in others, multiple defects are present. Renal tubular disorders may be congenital
or acquired, the congenital disorders all being very rare. Chemical
investigations are needed for specific identification of these abnormalities
and may include amino acid
chromatography, or investigation of
calcium and phosphate metabolism, or
an oral glucose tolerance test (OGTT). The functions tested most often are renal concentrating power and the ability to produce an acid urine.
The
healthy kidney has a considerable reserve capacity for reabsorbing water, and
for excreting H+ and other ions, only exceeded under exceptional physiological loads. Moderate impairment of renal function may reduce this reserve, and
this is revealed when
loading tests are used to stress the
kidney. Tubular function tests are only used when there is reason to suspect
that a specific abnormality is present.
Fluid
deprivation test
This test is effectively a bioassay of vasopressin, which is itself difficult to measure. The test
can be hazardous in a
patient excreting large volumes of dilute
urine, and requires close supervision. There
are a number of ways of performing a fluid deprivation
test, differing in detail but all involving fluid deprivation over several
hours, ensuring that the patient
under observation takes no fluid, and
that excessive fluid losses do not occur. Local directions for test performance should be
followed. For instance, beginning at 10 pm,
the patient is told not
to drink overnight, and urine specimens are collected while the patient continues not to drink
between 8 am and 3 pm the next day. During the test, the patient should be weighed every 2 h,
and the test should be
stopped if weight loss of 3-5% of total
body weight occurs. Blood and urine specimens
are collected for measurement of osmolality. Normally,
there is no increase in plasma osmolality
(reference range 285-295 mmol/kg) over the period of water deprivation, whereas urine osmolality rises to 800 mmol/kg or more. A rising plasma osmolality and a failure to concentrate urine are consistent with either a failure to
secrete vasopressin or a failure to
respond to vasopressin at the level
of the distal nephron. When this pattern
of results is obtained, it is usual to proceed immediately to perform the DDAVP test.
DDAVP
test
The patient is allowed to drink a moderate amount of water at the end of the fluid deprivation
test, to alleviate thirst. An intramuscular injection
of DDAVP is then given, and urine specimens
are collected at hourly intervals for a further 3 h and their osmolality measured.
Interpretation of tests of renal concentrating
ability
These
tests are of most value in distinguishing among hypothalamic-pituitary,
psychogenic and renal causes of polyuria (Table 4.3).
Patients
with diabetes insipidus of hypothalamic-pituitary origin produce insufficient vasopressin; they should therefore not respond to fluid deprivation, but should respond to the DDAVP. As a rule, these patients show an increase in plasma osmolality during the fluid deprivation test, to
more than 300 mmol/kg, and a low urine osmolality (200-400 mmol'Kg). There is
a marked increase in urine osmolality,
to 600 mmol/kg or more, in the DDAVP
test.
Patients
with psychogenic diabetes insipidus should
respond to both fluid deprivation and DDAVP. In practice, however, renal medullary hypo-osmolality often prevents the urine osmolality from reaching 800 mmol/kg after fluid deprivation or DDAVP injection in these tests, as is normally
performed. Also, the chronic suppression of the physiological mechanism that
controls vasopressin release may impair the
normal hypothala-mic response to dehydration. These patients have a plasma osmolality that is initially low, but which rises during the tests. However, fluid deprivation
may have to be continued for more than
24 h in these patients before medullary hyperosmolality is restored;
only then do they show normal responses to fluid deprivation or to DDAVP
injection.
Polyuria
of renal origin may be due to inability of the renal tubule to respond to vasopressin, as in nephrogenic diabetes insipidus. In this
condition, there is failure to produce a concentrated urine in response either to fluid deprivation or to DDAVP injection, the urinary osmolality usually remaining below 400 mmol/kg; in these patients, plasma osmolality increases as a result of fluid
deprivation.
Fanconi's syndrome
Fanconi's
syndrome may be inherited (e.g. in cystinosis) or secondary to a number of other disorders (e.g. heavy metal poisoning, multiple myeloma). The syndrome comprises multiple defects of proximal tubular function. There are
excessive urinary losses of amino acids (generalised amino aciduria),
phosphate, glucose and sometimes HCO3,
which gives rise to a proximal renal tubular
acidosis. Distal tubular functions may also be affected. Sometimes
globulins of low molecular mass may be
detectable in urine, in addition to
the amino aciduria
RENAL REGULATION OF ACID-BASE BALANCE
The kidneys help to regulate the blood pH, together with
respiratory system and the blood buffer systems. Blood buffer systems very
quickly react to violation of pH (in 0.5-1 min); lungs influence on hydrogen
ions concentration in 1-3 min ; and kidney is the latest regulator of pH (in
10-20 hours). There are 2 main mechanisms which are responsible for the kidneys
regulation of blood pH: reabsorption of sodium and secretion of hydrogen ions.
1) Reabsorption of sodium ions during
transformation the alkaline phosphate Na2HPO4 of the blood
to the acidic phosphate (NaHPO4) which is eliminated in the urine.
2) When the urine is acidic, HCO3-
combines with H+ to form carbonic acid. Carbonic acid in the
filterate is then converted to CO2 and H2O by the action
of carbonic anhydrase. Carbonic acid dissociates to HCO3-
and H+. Then H+ (acid) excreted in the urine and HCO3-(base)
passes in to the blood as NaHCO3 and decreases the acidity.
3) Ammonia (NH3) is a base that is formed
from the amino acid glutamine within the tubular cells. It crosses into tubular
lumen to combine with H+ to form ammonium (NH4). This
effectively prevents accumulation of H+ ions in the fluid, and
therefore permits continued exchange of H+ for Na+ ions.
The amount of Na+ ions abbsorbed in the distal tubule is consequently
reflected in the amount of both H+ and NH4+
ions in the urine.
8. Properties
and urine’s composition
The amount of urine
(diuresis) excreated by a healthy man is 1000-2000 ml per 24 hours. Daily amount
of urine, which is lower than 500 ml and higher than 2000 ml, of adults is
considered to be pathological. Men's diuresis is a little bit higher than
women's one, and it is 1500-2000 ml, and women's diuresis is 1000-1600 ml.
Twenty four hour's diuresis can change depending on the kind of a diet,
conditions of work, the temperature of the environment and ets.
Drinking a lot of water
causes the increase of diuresis to 2000-3000 ml, and decrease of water drinking
causes the decrease of diuresis to 700 ml and even less. Consuming of fruits,
berries and vegetables, rich in water also increase diuresis, but dry products,
especially salted, lower it. The volume of urine is also lowered during a work
in hot shops when a man loses water mostly through sweating.
Diuresis's increase
(poliuria) is observed with many diseases and while using different diuretics. A lot of urine is
excreted by the patient who are ill with diabetes mellitus and
diabetes insipidus.
Twenty four hour's
decrease of urine excretion (oliguria) is observed while having fever, diarhea,
nausea, acute nephritis, heart deficieny and in some other cases.
When a man is lead or
arsenic poisoned, is upset, has nephritis, the full stop of urine excretion
(anuria) is observed. Prolonged anuria causes uremia. According to standard,
urine is discharged 3-4 times more by day – light time than at night. But in
some pathological conditions (the beginning of heart decompensation, diabetes,
nephritis) become apparent by predominance of night discharge compare to day
time. Such condition is called nicturia.
Urine’s colour. Usually urine is straw -yellow. It's main pigment is urochrome which is
formed from urobilin or urobilinogen during their interaction with some peptides.
Some other pigments influence on the urine's colour, that's uroerytryn which is
obviously derivate of melanin, uroporphyrins, riboflavin and others. During the
conservation obviously as a result of urobilinogen oxidation, urine darkens.
Such urine is observed during bilirubin's excretion when a man is ill
with obstructive or hepatic jaundice.
Concentrated urine,
which is excreted in large quantities and has high specific gravity, is of
bright-yellow color.
Pale urine has low
specific gravity and is excreted in large quantities.
Urine can become of
different colour shades when a patient has pathological changes. Urine is red
or pink-red when a patient is ill with hematuria, hemoglobinuria, when he takes
amidopirin, santonin and other medicines. High concentration of urobilin and bilirubin can cause dark-red
colour of urine.Green or blue colour of urine is observed while albumin is
rotting in the bowels and as a result, indoxylsulphuric acids are produced. The
last ones while decomposing produce indigo.
Transparency. Fresh urine is transparent. Not fresh urine opacificates because of
mucins and the epithelium of the mucosal membrane of urethras. Urine's opacification is caused
also by the crystals of oxalic acid (oxalates) and uric acid (urates). During
durable urine standing mostly urates are in fall-our, which, adsorpting
pigments, cause its opacification. Calcium and magnesium phosphates are in fall-out in urine with alkaline
reaction. Alkaline character of urine which is falling out is caused by the decomposition of urea under
the influence of urine's microflora to ammonia. Ammonia makes urine alkaline
that causes the fall-out of mentioned solts and urine's darkening.
Urine also becomes
turbid when a patient is ill with inflamatory process of urethra ducts while
pus, proteins, blood cells falling into urine.
For the diagnostics of
some diseases urine is acidified and warmed up. If after this process
cloudiness disappears it means that it is caused by calcium or magnesium
phosphates or urates. If cloudiness
doesn't disappear it means that
it is caused by pus, epitheliym cells and by other admictures.
Urine's specific gravity depends on the concentration
of dissolving substances. During twenty
four hours urine's density changes from 1.002 to
Increase of the density during a normal
diuresis or poliuria is observed with that patients who discharge a great
amount of organic and nonorganic substanses. Urine of the person with diabetes
mellitus contains sugar, ketone bodies and other substances, which cause not only poliuria,
but a high density ( to 1.035). Daily diureses with low specific density of
urine is observed among the patients with diabetes insipidus. Urine with low
density which is similar to primary urine (1.010) is constantly discharged when a person has a complicated form of renal
failure. Such condition is called sthenuria, and it speaks about the
disturbance of the concentrational functions of kidneys.
Low density of urine
which have patients with diabetes incipidus (1.001-1.004) is the result of the
disturbance of reverseble reabsorption
of water in kidney's canaliculi becouse of lack of antidiuretic hormone.
Oliguria which
accompanies acute nephritis is characterized with high urine's density
Urine's reaction. Normally, having mixed food urine is acidic or light acidic
(pH=5.3-6.8). Urine with pH=6 is usually taken as the norm. Eating mostly meat
food and proteins gives urine acidic reaction, while eating vegetables it
become alkaline. Acidic reaction of urine is mainly caused by onesubsubstituted
phosphaties, mostly NaH2PO4 and KH2PO4. Twosubstituted phosphaties or
biocarbonate potassium or sodium predominate in alkaline urine. Considerable
emimence of alkaline substances in blood is accompanied with biocarbonates
excretion with urine that raises pH from 6.0 to 7,5-7.7.
Alkaline reaction of
urine is observed in patients who are ill with the cystitis (inflammation of
urinary bladder) which is connected with urea decomposition and ammonia
formation.
The same reaction is
observed after vomiting, drinking of alkaline mineral waters and so on.
Clearly acidic reaction
is notable for patients who are ill with diabetes mellitus, during fever and
starvation.
Urine's smell. Fresh urine has a specific smell mainly caused by volatile acids which
are available in it. Urine which is preserved, is influenced by microorganisms,
specifically by the decomposition of urea with ammonia forming. The last one
causes acute ammonia smell. Healthy people's urine can have different smell,
depending on kind of meals. Having some garlic, horseradish, onion gives urine
specific smell. Taking medicines and also some diseases can give urine
specific smell to.
8.1 Chemical
composition of the urine
There are a lot of different
organic and non- organic substances in the urine (about 200 ).
They are metabolism end-
products in the kidneys and other organs
and tissues of the organism.
8.2 Organic components of the urine
Proteins. Healthy man
excretes about 30 mg of proteins with urine per day. This quantity of the
protein is not determined by ordinary lab. methods. As a rule low molecular
proteins are eliminated , such as enzymes( pepsin, trypsin , amilase, ets.) ,
albumins. The increasing of protein level in urine is called proteinuria. There
are 2 kinds of proteinuria: renal (real) and extrarenal (unreal or false).
Renal proteinuria is caused by organic demage
of nephrons , due to blood proteins
(albumins and globulins) occur in urine. For example inflammation of
glomeruluses (glomerulonephritis )or nephrosis (violations of proteins
reabsorption in tubules).
Extrarenal proteinuria- availability of
proteins in urine due to diseases of urinary tract. (inflammation of urinary
bladder, urethritis). Patients with such diseases may loose 20
Urea is the main
end- product of the catabolism of
amino acids and is the substance in which is incorporated , for purposes of
excretion, the bulk of the nitrogen provided to the organism in excess of its
needs. Nitrogen of urea is equal to 80
-90 %of total nitrogen in urine.
An
adult eliminates 20-
The
increasing of urea concentration:
1. Excess of proteins in the diet
2. Diabetes mellitus
3. Cancer
4. Fever
The
decreasing of urea concentration:
1. Lack of
proteins in the diet
2. Liver
diseases
3. Acidosis
4.
Intensive growth of the organism
Pre-renal uraemia may develop whenever there is impaired renal perfusion, and is essentially the result of a physiological response to hypovolaemia or a drop in blood pressure. This causes renal
vaso-constriction and a
redistribution of blood such that
there is a decrease in GFR, but preservation of tubular function.
Stimulation of vasopressin secretion and of
the renin-angiotensin-aldosterone system
causes the excretion of small volumes of concentrated urine with a low Na content. This reduced urine flow in turn causes increased passive
tubular reabsorption of urea. Thus shock, due to
burns, haemorrhage or loss of water and electrolytes (e.g. severe diarrhoea) may lead to increased plasma [urea]. Renal blood flow also
falls in congestive cardiac failure,
and may be further reduced if such patients are treated with potent diuretics. If pre-renal uraemia is not treated adequately and promptly by restoring renal perfusion, it can progress to intrinsic renal failure.
Increased
production of urea in the liver occurs on high protein diets, or as a result of
increased protein catabolism
(e.g. due to trauma, major surgery, extreme starvation). It may also occur after haemorrhage into the upper GI tract, which
gives rise to a 'protein meal' of
blood.
Plasma
[urea] increases relatively more than plasma [creatinine] in pre-renal uraemia. This is because tubular
reabsorption of urea is increased significantly
in these patients, whereas relatively little reabsorption of creatinine occurs.
Renal uraemia may be due to acute or chronic renal failure, with reduction in glomerular
filtration. Plasma [urea] increases until a new steady state is reached at which urea production equals
the amount excreted in the urine, or continues to rise in the face of near-total renal failure. Although frequently measured as a test of renal function, it is always important to remember that
plasma [urea] may be increased
for reasons other than intrinsic
renal disease (pre-renal and post-renal uraemia).
Post-renal uraemia occurs due to outflow obstruction, which may occur at different levels (i.e. in the
ureter, bladder or urethra), due
to various causes (e.g. renal stones, prostatism, genitourinary cancer).
Back-pressure on the renal tubules enhances
back-diffusion of
urea, so that plasma [urea] rises disproportionately
more than plasma [creatinine]. Impaired
renal perfusion and urinary tract obstruction,
each in itself possible causes of uraemia,
may in turn cause damage to the kidney and
thus renal uraemia.
Uric acid:
An adult eliminates 0.6 - 1g
of uric acid with urine per day.
The
increasing of uric acid concentration:
1. Feeding products, which contain many
nucleoproteins(meat , fish eggs etc)
2. Leucosis, burns
3. Some Drugs (Aspirin)
4. Violations of proteins metabolism (gout)
The decreasing of uric acid concentration:
1. Diet poor in proteins and rich in carbohydrates
Intermediate products of purine metabolism are also
excreated with urine (xanthine, hypoxanthine – 20-50 mg per day).
Creatinine
and Creatine:
An adult excretes of 1-
Synthesis of creatine, from which creatinine is
formed, is in the kidneys and liver. The decreasing concentration:
1. The kidneys and the liver lesion
2. Violations of protein metabolism
3. Atrophy of muscle
Creatinine is neither reabsorbed nor secreted by the
tubules, the amount excreted per minute in the urine will be equal to the
amount that is filtered out of the glomeruli.
Creatinine is used for the determination of renal
plasma clearance.
The increasing of the creatinine concentration:
-Some infections
-Intoxications
The decreasing of creatinine concentration:
- Violations of filteration in kidneys. Children
excrete more creatine than adults, females- more, than males.
Cretinuria takes place in old people due to muscle
atrophia .
Amino Acids:
An adult excretes about 2-
1. Splitting of the tissue proteins
2. Violations of liver functions
There are some genetic defects in the metabolism of
seperate amino acid. For example:
1) Phenylketonuria: Which is caused by enzyme phenylalanine-4-monoxygenase
absence. In this case a pathway of phenylalanine breakdown and tyrosine is not
formed. To determine phenylketonuria is used FeCl3 ( fresh urine +2-3 drops of
FeCl3 solution and in 2-3 min observe appearance of dark-green colour).
2) Alkaptonuria: The urine of people genetically
defective in homogentisic acid 1,2-dioxygenase contains homogentisic acid,
which when made alkaline and exposed to oxygen, turns dark because it is
oxidised and polymerized. to a black melanine pigment.
Paired
compounds:
Hippuric acid (benzoglycine) is formed by the
conjugation in peptide linkage of benzoic acid and glycine. In a man this
occours largely in the liver and also in the kidneys. Benzoglycine is excreted
in the urine in amounts ranging from 0.6 to
Indican : It
is excreted in the urine in amounts ranging from 10-25 mg daily.
The
increasing of indican concentration :
1. Intestinal obstruction
2
Generalized peritonitis.
3.
Decomposition of tissue protein, for example, tuberculosis
Organic
compounds:
In the urine of healthy man some organic acids are
usually observed (for example, acetoacetate ). Some lipids (cholesterol) are
present in urine in small amounts.
Vitamins:
Allmost all vitamins are excreted with urine. Most
of all water-soluble vitamins such as thiamine: 0.1-0.3mg, riboflavin:
0.5-0.8mg ,ascorbic acid: 20-30mg . In medicine wide-spread is a method of determining
quantity mg. of vitamin C,which is excreted in urine per hour.In a person 1mg
of vitamin C is excreted per hour.
Hormones:
Some hormones
are present in urine. Androgenic compounds of 17- ketosteroids structure are
found in the urine of normal person in amounts ranging from 15-25 mg. The
increasing of this quantity may be caused by adrenocortical tumours.
Urobilin (stercobilin): always is
present in small amounts in urine. It's concentration increases when liver
looses property to decompose urobilinogen from intestine(haemolytic jaundice
and hepatic jaundice).
Bilirubin:
Urine of
healthy individual contains a small amount of bilirubin, which is not
determined by ordinary lab. methods.
Causes of
bilirubinuria:
1. Obstruction of bile canaliculi and bile duct.
2. Damage of liver cells.
Urine will
have special colour like dark beer, then it becomes yellow-green, due to
oxidation of bilirubin into biliverdin.
Glucose:
Urine of
healthy person contains small amounts of glucose, which is not determine by
urinary lab methods.
Glucose is
normally completely reabsorbed in the proximal tubule. But in the patient with
diabetes mellitus , content of glucose in urine may be 5-10%.
Galactose:
Galactose is metabolised mainly by liver. Alimentary
galactosuria, which is related to the ingestion of milk and milk products.
In new borns galactosuria very often combines with lactosuria.
Galactose tolerance:
After
ingestion of 40 mg. of galactose , quantity of galactose is detected in urine
per every hour.
In normal
conditions galactose is excreted in urine in first 2 hours.
Fructose:
Fructose
may appear in the urine under the following circumstances;
1. Alimentary fructosuria(fruits, berries, honey).
2. Unsatisfactory hepatic function.
3. Diabetes mellitus.
Pentose:
Pentose may appear in the urine under the following
circumstances;
1. Alimentary pentosuria, occuring in normal
individuals after the ingestion of large quantities of fruts which have high
quantity of pentose content (cherries, grapes, plums).
2.Essential Pentosuria.
It is
genetically determined, has a familial incidence.
Ketone bodies:
In normal
conditions daily urine content is 20-50mg of ketone bodies. It is not
determined by ordinary lab. methods.
Ketonuria
may occur in a variety of clinical conditions;
1. Diabetes mellitus (20-50mg per day).
2. Carbohydrate starvation.
3. Thyrotoxicosis and fever.
Blood:
When red
blood cells appear in urine ( hematuria), it means that there are some damage
of the kidney or urinary tract.
Hemoglobinuria -- presence of free hemoglobin in urine , is a result of
hemolysis (renal infarction, poisons).
Porphyrins:
These are red
pigments with a pyrolle structure , which are important components of
hemoglobin ,, myoglobin, cytochrome and catalysts.In normal conditions daily
urine contain very small amount of poryphyrin type I (300 mkg).
There are 3
isomeric etioporyphyrins , designated typeI, II, III.
Porphyrinuria may occur in a variety of clinical
conditions :
- some liver diseases
- intoxication
- intestine bleeding
- pernicious anemia
8.3 Mineral components of the urine
In normal
conditions daily urine contains 15 to
Sodium chloride is the most wide-spread non-organic
substance in urine. It is excreted in amounts ranging from 8 to
About
In normal conditions daily urine contains 2 to
Calcium and
magnesium:
In
normal conditions daily urine contains 0,1-
In normal conditions daily urine contains 0,03-
Such low Ca
and Mg concentration is because their
salts are poorly soluble in water.
Iron:
In normal conditions daily urine contains about 1 mg
of iron.
Excessive breakdown of erythrocytes in hemolytic
types of anemia causes the increasing iron concentration.
Phosporus:
Phosphorus
is excreted in urine as KH2PO4 or NaH2PO4.
Quantity of
excreted phosphate depends on blood pH:
1. Acidosis: Alkaline phophate (NaH2PO4) react with
acids and are transformed into acid phosphates(NaHPO4) which are eliminated in
the urine.
2. Alkalosis: Acidic phosphates (NaHPO4) react with bases
and are transformed into alkaline phosphates (Na2HPO4 ) which are eliminated in
the urine.
Sulphur:
Sulphur is
excreted in the urine as sulphates and paired compounds. In normal conditions
daily urine contains 2-
Ammonia:
The ammonia which is present in the urine is formed
in the kidneys from amino acids , such as glutamine and asparagine, for purpose
of neutralization of excreted acid.
Quantity of
ammonia salts is equal to 3-6% of total urinary nitrogen. Urinary ammonia is
increased in many conditions associated with acidosis( diabetes mellitus,
starvation , dehydration, etc.)
Microscopic
Examination of Urine
The
third part of routine urinalysis is the microscopic examination of the urinary
sediment. Its purpose is to detect and to identify insoluble materials present
in the urine.
Red
Blood Cells
In
the urine, RBCs appear as smooth, non-nucleated, biconcave disks measuring
approximately 7 mm in diameter. In concentrated
(hypersthenuric) urine, the cells shrink due to loss of water and may appear crenated
or irregularly shaped. In dilute (hyposthenuria) urine, the cells
absorb water, swell, and lyse rapidly, releasing their hemoglobin and leaving
only the cell membrane. These large empty cells are called ghost cells and
can be easily missed if specimens are not examined under reduced light. The
presence of RBCs in the urine is associated with damage to the glomerular
membrane or vascular injury within the genitourinary tract.
Normal RBCs
Microcytic
and crenated RBCs
White Blood Cells
WBCs
are larger than RBCs, measuring an average of about 12 mm in diameter.
The
predominant WBC found in the urine sediment is the neutrophil. Neutrophils are
much easier to identify than RBCs because they contain granules and multilobed
nuclei.
WBC clump
Epithelial Cells
It
is not unusual to find epithelial cells in the urine, because they are derived
from the linings of the genitourinary system. Unless they are present in large
numbers or in abnormal forms, they represent normal sloughing of old cells.
Three types of epithelial cells are seen in urine: squamous, transitional
(urothelial), and renal tubular.
Sediment-containing squamous, caudate transitional,
and RTE cells
Squamous epithelial
cells
Syncytia of
transitional epithelial cells
Bacteria
Bacteria
are not normally present in urine. However, unless specimens are collected
under sterile conditions (catheterization), a few bacteria are usually present
as a result of vaginal, urethral, external genitalia, or collection-container
contamination.
These contaminant bacteria multiply rapidly in specimens that remain at room
temperature for extended periods, but are of no clinical significance. They may
produce a positive nitrite test result and also frequently result in a pH above
8, indicating an unacceptable specimen. Bacteria may be present in the form of
cocci (spherical) or bacilli (rods).
Parasites
The
most frequent parasite encountered in the urine is Trichomonas vaginalis. The
Trichomonas trophozoite is a pearshaped flagellate with an
undulating membrane. It is easily identified in wet preparations of the
urine sediment by its rapid darting movement in the microscopic field. Trichomonas
is usually reported as rare, few, moderate, or many per hpf. When
not moving, Trichomonas is more difficult to identify and may
resemble a WBC, transitional, or RTE cell. Use of phase microscopy may
enhance visualization of the flagella or undulating membrane.
T.
vaginalis is a sexually transmitted pathogen associated
primarily with vaginal inflammation. Infection of the male urethra and prostate
is asymptomatic. The ova of the bladder parasite Schistosoma haematobium
will appear in the urine. However, this parasite is seldom seen in the United
States. Fecal contamination of a urine specimen can also result in the presence
of ova from intestinal parasites in the urine sediment. The most common contaminant
is ova from the pinworm Enterobius vermicularis.
Mucus
Mucus
is a protein material produced by the glands and epithelial cells of the lower
genitourinary tract and the RTE cells. Immunologic analysis has shown that Tamm-Horsfall
protein is a major constituent of mucus. Mucus appears
microscopically as thread-like structures with a low refractive index. Subdued
light is required when using bright-field microscopy. Care must be taken not to
confuse clumps of mucus with hyaline casts. The differentiation can usually be
made by observing the irregular appearance of the mucous threads. Mucous
threads are reported as rare, few, moderate, or many per lpf. Mucus is more
frequently present in female urine specimens. It has no clinical significance
when present in either
female or male
urine.
Mucus threads
Casts
Casts
are the only elements found in the urinary sediment that are unique to the
kidney. They are formed within the lumens of the distal convoluted tubules and collecting
ducts, providing a microscopic view of conditions within the nephron. Their
shape is representative of the tubular lumen, with parallel sides and somewhat
rounded ends, and they may contain additional elements present in the filtrate.
The most frequently seen cast is the hyaline type, which consists almost
entirely of Tamm-Horsfall protein. The presence of zero to two hyaline casts
per lpf is considered normal, as is the finding of increased numbers following
strenuous exercise, dehydration, heat exposure, and emotional stress.
Pathologically, hyaline casts are increased in acute glomerulonephritis,
pyelonephritis, chronic renal disease, and congestive heart failure.
Hyaline
casts appear colorless in unstained sediments and have a refractive index
similar to that of urine; thus, they can easily be overlooked if specimens are
not examined under subdued light. The morphology of hyaline casts is varied,
consisting of normal parallel sides and rounded ends, cylindroid forms, and
wrinkled or convoluted shapes that indicate aging of the cast matrix.
Convoluted hyaline cas
Hyaline cast containing occasional granules
RBC
Casts
Whereas
the finding of RBCs in the urine indicates bleeding from an area within the genitourinary
tract, the presence of RBC casts is much more specific, showing bleeding within
the nephron. RBC casts are primarily associated with damage to
the
glomerulus (glomerulonephritis) that allows passage of the cells through the
glomerular membrane; however, any damage to the nephron capillary structure can
cause their formation.
RBC
casts associated with glomerular damage are usually associated with proteinuria
and dysmorphic erythrocytes. RBC casts have also been observed in healthy
individuals following participation in strenuous contact sports.
RBC cast. Notice the presence of hypochromic and
dysmorphic free RBCs
WBC
Casts
The
appearance of WBC casts in the urine signifies infection or inflammation within
the nephron. They are most frequently associated with pyelonephritis and are a
primary marker for distinguishing pyelonephritis (upper UTI) from lower UTIs.
However, they are also present in nonbacterial inflammations such as acute
interstitial nephritis and may accompany RBC casts in glomerulonephritis.
Waxy
Casts
Waxy
casts are representative of extreme urine stasis, indicating chronic renal
failure. They are usually seen in conjunction with other types of casts
associated with the condition that has caused the renal failure. The brittle,
highly refractive cast matrix from which these casts derive their name is
believed to be caused by
degeneration
of the hyaline cast matrix and any cellular elements or granules contained in
the matrix.
Granular cast degenerating into waxy cast
Urinary
Crystals
Crystals
frequently found in the urine are rarely of clinical significance. They may
appear as true geometrically formed structures or as amorphous material. The
primary reason for the identification of urinary crystals is to detect the presence
of the relatively few abnormal types that may represent such disorders as liver
disease, inborn errors of metabolism, or renal damage caused by crystallization
of iatrogenic compounds within the tubules. Crystals are usually
reported as rare, few, moderate, or many per hpf. Abnormal crystals may be
averaged and reported per lpf. Crystals are formed by the precipitation of
urine solutes, including inorganic salts, organic compounds, and medications
(iatrogenic compounds). Precipitation is subject to changes in temperature,
solute concentration, and pH, which affect solubility. Solutes precipitate more
readily at low temperatures. Therefore, the majority of crystal formation takes
place in specimens that have remained at room temperature or been refrigerated
prior to testing. Crystals are extremely abundant in refrigerated specimens and
often present problems because they obscure clinically significant sediment
constituents. As the concentration of urinary solutes increases, their ability
to remain in solution decreases, resulting in crystal formation. The presence
of crystals in freshly voided urine is most frequently associated with
concentrated (high specific gravity) specimens.
A
valuable aid in the identification of crystals is the pH of the specimen
because this determines the type of chemicals precipitated. In general, organic
and iatrogenic compounds crystallize more easily in an acidic pH, whereas
inorganic salts are less soluble in neutral and alkaline solutions. An
exception is calcium oxalate, which precipitates in both acidic and neutral
urine.
Uric acid crystals
Classic dihydrate calcium oxalate crystals.
Amorphous urates
Amorphous phosphates
“Coffin lid” and other forms of triple phosphate
crystals
Cholesterol crystals. Notice the notched corners
Renal
Disease
Disorder |
Primary Urinalysis
Results |
Cystitis |
Leukocyturia Bacteriuria Microscopic hematuria Mild proteinuria Increased pH |
Acute pyelonephritis |
Leukocyturia Bacteriuria WBC casts Bacterial casts Microscopic
hematuria Proteinuria |
Chronic
pyelonephritis |
Leukocyturia Bacteriuria WBC casts Bacterial casts Granular, waxy, broad casts Hematuria Proteinuria |
Acute interstitial
nephritis |
Hematuria Proteinuria Leukocyturia WBC casts |
Acute
glomerulonephritis |
Macroscopic hematuria Proteinuria RBC casts Granular casts |
Chronic
glomerulonephritis |
Hematuria Proteinuria Glucosuria Cellular and granular casts Waxy and broad casts |
Nephrotic syndrome |
Heavy proteinuria Microscopic hematuria Renal tubular cells Oval fat bodies Fat droplets Fatty and waxy casts |
Renal failure
Acute renal failure
By definition, there
is renal disease of acute onset, evere enough to cause failure of renal homeostasis. Often oliguric, diuretic and recovery phases can be recognised, although a few patients
maintain a normal urine volume throughout the course of the illness. Chemical investigations help to determine
the severity of the disease and to follow its
course, but do not help much in determining the cause. Proteinuria is present,
and haem pigments from the blood may
make the urine dark.
Oliguric phase
In this phase, less than 400 mL urine is produced each day; if the renal failure is due to outflow restruction, there may be anuria. The oliguria is
mainly due to a fall in GFR.
The urine that is formed usually has
an osmolality similar
to
plasma and a relatively high [Na+],
since the composition of the small amount of glomerular filtrate
produced is little altered
by the damaged tubules.
Plasma [Na+] is usually low due to a combination of factors, including intake of water in excess
of the amount able to be
excreted, increase in metabolic water from
increased tissue catabolism, and possibly a shift of Na+ from ECF to ICE. Plasma [K+], on the
other hand, is usually increased due
to the impaired renal output and increased tissue catabolism, which aggravated by the shift of K+ out of
cells that acompanies the
metabolic acidosis that develops due to failure to excrete H+ and
also due to the increased
formation of H+ from tissue catabolism.
Retention of urea, creatinine, phosphate, sulphate
and other waste products occurs. The rate at which plasma [urea] rises is affected by the rate
of tissue catabolism; this, in turn,
depends on the cause of the acute renal failure. In
renal failure due to trauma (including renal
failure developing after surgical
operations), plasma [urea] tends to rise more rapidly than in patients with renal failure due
to medical causes such as acute
glomerulonephritis.
To
differentiate the low urinary output of suspected acute renal failure from
that due to severe circulatory
impairment with reduced blood volume,
the tests summarised in Table 4.4 may be helpful.
However, none of these tests can be completely
relied upon to make the important and urgent
distinction between renal failure and hypovolaemia. Careful assessment of the
patient's fluid status, possibly
including measurement of the central
venous pressure, is also required.
For
monitoring patients in the oliguric phase of acute renal failure, plasma [creatinine] or [urea] and
plasma [K+] are particularly important, and need to be determined at least once daily. Decisions to use haemodialysis are reached at least partly on the basis
of the results of these tests. The volume of
urine and its electrolyte composition (and the volume and composition of any
other measurable sources of fluid loss) should also be assessed in order to determine fluid and electrolyte replacement requirements.
Diuretic
phase
With
the onset of this phase, urine volume increases, but the
clearance of urea, creatinine and other waste products may not improve to the
same extent. Plasma [urea] and [creatinine]
may therefore continue to rise, at
least at the start of the diuretic phase.
Large losses of electrolytes may occur in the urine and require to be
replaced orally or parenter-ally.
Measurement of these losses is needed so that correct replacement therapy can be given; this requires urine collections, for urine [Na+]
and [K+] measurement, and
calculation of daily outputs. Plasma [K+] tends to fall as
the diuretic phase continues, due to the
shift of K+ back into the cells and to marked losses in urine resulting from impaired conservation of K+ by the still-damaged tubules. Usually, Na+ deficiency occurs
also, due to failure of renal
conservation. Throughout the diuretic phase, therefore, it is important to measure
plasma [creatinine] or [urea] and both plasma [Na+] and [K+]
at least once daily, and to monitor the
output of Na+ and K+ in the urine.
Chronic
renal failure
Most
of the functional changes seen in chronic renal failure can be explained in terms of a full solute load falling on a reduced number of
normal nephrons. The GFR is invariably reduced,
associated with retention of urea,
creatinine, urate, various phenolic
and indolic acids, and other organic substances.
The progress and severity of the disease
are usually monitored by measuring plasma [creatinine] or [urea], or both.
Sodium, potassium and water
The renal handling of Na+, K+ and water by normal kidneys and in chronic renal failure has already been considered above.
Acid-base disturbances
The total excretion of H+ is impaired, mainly due to a fall in the renal capacity to form NH4+.
Metabolic acidosis is present in
most patients, but its severity
remains fairly stable in spite of the reduced urinary H+
excretion. There may be an extrarenal mechanism for H+ elimination,
possibly involving buffering of H+
by calcium salts in bone; this would
contribute to the demineralisation of bone
that often occurs in chronic renal failure.
Calcium and phosphate
Plasma
[calcium] tends to be low, often due, at least partly, to reduced plasma [albumin]. Plasma [phosphate]
is high, mainly due to the reduction of GFR. Virtually all patients with chronic renal failure have secondary or, much less often, tertiary hyper-parathyroidism,
and they may develop osteitis fibrosa. Plasma [calcium], which is decreased or
close to the lower reference value in patients with secondary
hyperparathyroidism, increases later if tertiary hyperparathyroidism develops. Many patients with a low plasma [calcium] have reduced activity of renal cholecalciferol la-hydroxylase,
the enzyme responsible for the synthesis of the most active form of vitamin D.
They can potentially develop osteomalacia or rickets, but this would be uncommon in adequately treated patients. A few patients show a third type of bone
abnormality: increased bone density (osteosclero-sis). It is not clear
why any particular one of these various types
of renal osteodystrophy should develop
in an individual patient.
Renal
stones
Physicochemical
principles govern the formation of renal stones, and are relevant to the choice
of treatment aimed at preventing
progression or recurrence.
Stones may cause renal damage, often progressive.
The
solubility of a salt depends on the product of the activities of its constituent ions. Frequently,
the solubility product in urine is exceeded without the formation of a stone, provided there is no 'seeding' by particles present in urine, such as debris or bacteria, which promote crystal formation. Formation of stones can also be prevented
by inhibitory substances that are
normally present in the urine, such
as citrate, which can chelate calcium, keeping it in solution.
People
living or working in hot conditions are liable to become dehydrated, and show a
greater tendency to form renal
stones, as the urine becomes more
concentrated. There are also several metabolic
factors.that can cause stones to form in the renal tract. However, in many patients, no cause can be found to explain why stones have formed.
URGENT LABORATORY ANALYSIS
The
doctor who is faced with a patient in ambulance, which suddenly fell ill, must
think and act quickly. Proper implementation of the urgent laboratory analysis
is a very valuable help for early diagnosis and treatment. All clinical
biochemistry laboratories provide facilities for urgent tests. An urgent test
is designated as one on which the clinician is likely to take immediate action.
The main reason for asking for an analysis to be performed on an urgent basis
is that immediate treatment depends on the result.
On
the other hand, excessive or inappropriate laboratory investigations leading to
the loss of valuable time and resources and can delay the start of treatment.
The main indications for urgent
biomedical investigations:
• Establishing a diagnosis in case of sudden
illness.
• Assessment of severity of disease.
• Assessment of prognosis of the disease in
the near future.
• Monitoring effects of treatment applied.
Urgent laboratory tests should be:
•
available 24 hours a day;
• performed quickly enough to be useful for
the physician;
• meet the clinical problems arising from the
sudden illness.
Urgent
tests hinder the planned laboratory work during the day, and their performance
in leisure time is very expensive. Although some tests such as determination of
glucose in the blood can be performed in hospital departments or in the
reception rooms, most of the studies should be conducted by trained personnel
in specially equipped laboratories duty. Therefore, guidance on carrying out
urgent tests in the laboratory should be given only when the result of analysis
can directly influence the way of the patients’ treatment.
Urgent
biochemical investigations
The investigation of blood
• Urea and electrolytes (sodium,
potassium),chloride, bicarbonate (hydrocarbons) or total
CO, and creatinine.
• Glucose.
• Detection of blood gases (pH or concentration
of ions of hydrogen, pO2, ðÑÎ2).
• Osmolality (can
be used in case of acute poisoning, when it is not
possible to determine the alcohol content).
• Amylase.
• Salicylates.
• Paracetamol.
The investigation of urine
• Osmolality
• Sodium.
• Urea (it
is nessesary to
determine whether the fluid that
collects in the abdomen, is urine or not).
• The presence of opiates.
• Ketone bodies (qualitative analysis).
• Diagnosis of pregnancy.
The
Investigation of cerebrospinal fluid
• Protein.
• Glucose.
Other
studies:
The
availability of other tests in urgent cases depends on the specific hospital or
laboratory, as well as the specific circumstances and needs. For example,
toxicological laboratory can offer a wider range of drugs’ content
investigation. In many laboratories after appropriate approvals can determine
the concentration of theophylline, digoxin, lithium. In patients with carbon
monoxide poisoning the concentration of carboxyhaemoglobin is determined.
Determination
of iron levels in serum may be necessary if it was an overdose. This test is
important especially for children who have iron overdose which is especially
dangerous. Determination of lactate in whole blood is difficult to perform in
urgent cases, although some laboratories perform less accurate determination of
lactate in plasma obtained from whole blood, typed into tubes containing
fluorides and oxalates. Determination of lactate level is rarely used to
diagnose lactic acidosis. If the lying-in hospital contains Intensive Care
department, in urgent cases should further determine the level of calcium,
magnesium and bilirubin. To assess preeclampsia states should be performe
investigation of urea in blood serum.
"Acute abdomen"
Emergency
abdominal disease, united as "acute abdomen", often requiring immediate
surgery. The purpose of biomedical investigations in these cases are:
1.
Diagnosis;
2.
Get answers to questions:
-Is
there a need to operate patient immediately;
-What
to do to prepare the patient for surgery, if necessary, and if not, then:
-kind
of therapeutic treatment should be applied.
In
all patients with symptoms of acute abdominal pain it is nessesary to determine
the level of urea and electrolytes in blood serum. Electrolyte concentration
outside the normal range may indicate a loss of extracellular fluid in the
digestive tract, tissue damage, or loss of renal origin: uremia may indicate
dehydration or the beginning of the internal kidney damage, low bicarbonate
(sometimes referred to as "total CO2") may indicate
beginning of lactic acidosis caused by tissue hypoxia and shock. Sometimes it
is need to determine the level of glucose in the blood or plasma: diabetic
ketoacidosis often is manifested by pain
in the upper and middle abdomen. In patients with clinical signs of shock, be
sure to hold investigations of gases that have confirmed or excluded violation
of acid-base balance and (or) hypoxia. The investigation of amylase activity in
serum is often used to diagnose acute pancreatitis.
Although
there are many causes of elevated diastase, but more than four-fold increase in
amylase activity in patients with symptoms of acute abdominal pain and signs of
peritonitis may indicate acute pancreatitis before the diagnosis is not
confirmed by other diagnostic methods. But we must remember that normal value
or moderate increase in serum amylase not exclude acute pancreatitis and
hypergliceremiya which is often associated with diseases of the pancreas may
lead to an artificial decrease of amylase in serum.
Loss of consciousness
Differential diagnosis of states of unconsciousness in patients may be classified as follows:
1. Reasons related
to the central nervous system:
-vascular brain disorders: bleeding in the brain and subdural
hemorrhage;
-head injury;
-inflammatory states: encephalitis, meningitis;
-brain abscess;
-other brain lesions
(tumors).
2. Overdose of
drugs that cause central nervous
system depression or significant metabolic disturbances.
3. Metabolic causes:
-acute acidosis (regardless of reason);
-dehydration;
-endocrine disorders: adrenal crisis (acute
adrenal insufficiency) with Addison's disease, thyroid crisis (myxedema);
-hyperglycemia, diabetic coma;
-hepatic encephalopathy;
-in children: congenital metabolic defects.
In all cases, biochemical investigations should be
based on detailed assessment of the clinical condition of the patient. If even
the reason of loss of consciousness is
trauma of the head, we must remember that the patient may lose consciousness
before the injury on each of the above reasons. In all unconscious patients is
need to determine the level of glucose, urea, electrolytes in serum and blood
gases. Other investigations such as determining the level of alcohol (or
osmolality), paracetamol, salicylates, analysis of cerebrospinal fluid and
others should depend on the clinical condition of the patient.
Acute metabolic violations in
diabetes mellitus
Acute
metabolic violations in diabetes mellitus:
-ketone acidosis and coma (ketoacidosis);
-lactatic acidosis and coma, which can coexist
with ketone coma;
-hypoglycemic coma.
Patients
with ketone coma similarly complain of feeling unwell for several days. There
may be signs and symptoms of the reasons that led to metabolic decompensation,
such as infection, trauma, stress. You can even suggest a low tolerance to
insulin, but in 50 % of cases the cause of sudden decompensation remains
unknown. Clinically there is impairment of consciousness, the patient felt
about the characteristic smell of acetone (though not everyone can feel it).
Breath is deep and noisy (Kussmaul
breathing). Biochemical diagnosis of all patients with suspected diabetic
ketosis should include determination of
blood gases (to determine the degree of metabolic acidosis), the level
of glucose in plasma or whole blood (to confirm hyperglycemia) and the
concentration of urea and electrolytes (because patients observed loss of
water), sodium and potassium. Potassium levels may be high due to speciation
acidosis and reduced glomerular filtration. Semi-quantitative analysis using
paper tests can be used to confirm the presence of ketone bodies in plasma or
serum. Further investigation after the start of treatment should include
determination of glucose and potassium at least every 2 hours during the first
6 hours of treatment and determine the pH if acidosis was profound.
Lactic acidosis -
a serious complication of diabetes mellitus with high mortality (about 50 %).
It can occur in patients with type II diabetes treated with biguanidyn
derivatives, coexisting with kidney failure or liver disease. Often lactic
acidosis appear during acute conditions such as shock, ketosis, myocardial
infarction, burns or multiple trauma. If lactic acidosis is accompanied by
ketoacidosis, the consequences are very severe because of the reduced buffer
capacity of blood, leading to a profound acidosis. Previous biochemical studies
are the same as for ketone coma, though you can not detect the presence of
ketone bodies, or they may appear only in small quantities. In case of doubt
regarding the diagnosis should be determined lactate concentration in plasma
and its level over 50 mmol/l is a diagnostic sign of lactic acidosis.
Hypoglycemic
coma may occur in every patient with diabetes that is treated with insulin or
in patients with diabetes type II, which are treated with sulfonylurea
derivatives. Often the cause is an error in the dosage of insulin, food in the
wrong time, excessive physical effort, which did not provide additional supply
of carbohydrates, or reduce the use of glucose and alcohol, which inhibits
gluconeogenesis. Usually hypoglycemiya begins suddenly, and the patient becomes
dizzy, disoriented, and in severe cases may even lose consciousness. The brain
uses glucose as almost the only source of energy. Clinical signs resulting from
reduction of glucose in the brain. After the acute event or after many cases of
hypoglycemia occur lasting brain damage. In these patients, hypoglycemia can be
diagnosed by determining glucose in serum or blood. Treatment consists of oral
or intravenous glucose or glucagon injection (intramuscularly, subcutaneously
or intravenously).
Urgent hematological investigations
Immediate laboratory analysis
should include the morphological study of blood, which consists of
determination of:
-Hemoglobin concentration (analysis to evaluate the degree of anemia and
control efficiency hemotherapy);
Hematocrit (to assess the degree of anemia and has the same diagnostic value as
the concentrations of hemoglobin);
-Number of leukocytes (increased white blood cell count (leukocytosis)
indicates leukocyte reaction system in inflammatory conditions and bacterial
infections; analysis helps diagnose the state of "acute abdomen" and
decide on the need for surgery in a matter of urgency, reduce the number of
leukocytes (leukopenia) may be the cause or the result of severe viral
infections);
-Platelets (may help determine the cause of acute hemorrhagic diathesis);
-Peripheral blood smear (especially leukocyte rating system that has diagnostic
value in the process where the number of leukocytes within the normal
assessment jet shifts to the left allows you to detect infection and evaluate the
degree of its severity;
evaluation of blood smear is of
particular importance for differential diagnosis of acute infectious diseases
in children).
The proposed above set of tests
to evaluate the pathological conditions that require a doctor's application for
immediate action. These states are:
-Acute blood loss;
-Hypovolemic shock;
- "Acute abdomen";
-Septic shock;
-Acute infection;
Syndrome of disseminated
intravascular coagulation (DIC).
Acute blood loss
Acute blood loss
is one of the most common pathological conditions that require immediate
response laboratory. The reason for the sudden loss of blood may be an external
post-traumatic bleeding with tissue damage and large arterial vessels, internal
bleeding in the abdomen or chest, surgery, bleeding from the digestive tract,
as well as genitals (during pregnancy or childbirth). Acute bleeding may occur
also in the course of hemorrhagic diathesis, tumors, leukemias. Determination
of blood loss is difficult and largely based on clinical symptoms. Depending on
the flow dynamics of the patient can move up to 50 % loss of circulating blood,
if this loss continues more than 24 hours.
Sudden loss of 30 % of blood volume can lead to death of the patient.
Immediately after the onset of bleeding, hemoglobin concentration and
hematocrit value may not be affected. Normocytic anemia is detected by
laboratory methods only a few to a dozen hours after the sudden loss of blood.
The earliest sign of this is the growing number of platelets (an hour) and
leukocytes from leukocyte rejuvenation system (2-5 hours). In case of
bleeding, which occur less sharply, the level of hemoglobin or hematocrit
allows to establish the degree of severity of the disease. Introduction of
patient weighing
Hypovolemic shock
The
cause of hypovolemic shock may be blood loss (hemorrhagic shock) or loss of
plasma, water or electrolytes. Laboratory analysis that help in the diagnosis
of shock - it is the concentration of hemoglobin and hematocrit index (changes
appear in a few hours after blood loss), parameters of coagulation and the
activity of amylase and lipase.
"Acute abdomen"
In
addition to biochemical changes characteristic of "acute abdomen"
frequent symptom is increasing the number of leukocytes. Jet shift to the left of
granulocyte accompanying leukocytosis may be a sign of infection-purulent
process in the abdominal cavity. Growth shift to the left in the peripheral
blood smear shows the progression of purulent process and at other obscure
clinical signs from the side of the abdomen may indicate the need for surgery.
Septic shock
Septic
shock can occur in the course of infections caused by gram-positive and
gram-negative bacteria, less viruses, parasites or fungi. In addition to
clinical symptoms of shock, such as fever, chills, hyperventilation and
impaired consciousness, characterized by the following laboratory findings,
leukocytosis or leukopenia as that accompanied by a shift to the left,
thrombocytopenia and hypophosphatemia. When septic shock syndrome is accompanied
by DIC syndrome, but thrombocytopenia, a decrease in fibrinogen levels and
increase the number of fibrinogen degradation products is observed.
Acute infection
Clarify
the reason of acute infections,
especially in children, has important prognostic value and impact on the way of
treatment. Set etiological factor by bacteriological or virological research is
time-consuming. Study leukocyte system, especially the peripheral blood smear
may provide information about the type of etiological factors. Infants and
small children are particularly sensitive to any infection increase the number
of leukocytes. Bacterial infection, especially purulent, followed by
granulocyte reaction, which manifests itself in the peripheral blood smear
significant shift to the left, up to and including myeloblasts (leukaemia
reaction). In turn, response of lymphocytes is a characteristic of many viral
infections. The possibility of early detection of type of etiological factor of
infection suggests the study of peripheral blood smear urgent analysis, which
facilitates the immediate conduct of appropriate treatment.
Syndrome of disseminated
intravascular coagulation (DICS)
This
syndrome may accompany maternity complications, intravascular hemolysis,
sepsis, viremia, cancer, leukemia, burns, crush syndrome, liver disease and
blood vessels. Various clinical and non-specific symptoms (fever, decreased
blood pressure, acidosis, proteinuria, hypoxia) is not sufficiently common to
the correct diagnosis. A characteristic feature is the appearance of
hemorrhagic diathesis (petechiae, ecchymosis, discharge from the wound) or
diffuse intravascular coagulation. Laboratory studies performed in a matter of
urgency, can observe the dynamics of change and make possible rapid
intervention.
Urgent
coagulation investigations
Each laboratory duty must be carried out such investigations of coagulation
that can diagnose acute bleeding, monitor the treatment of heparin, oral
anticoagulants and streptokinase, and quickly diagnose the syndrome of disseminated
intravascular coagulation (DIC).
Urgent Laboratory should be able to determine:
1. Activated partial thromboplastin-time;
2. Prothrombin time;
3. Thrombin time;
4. The number of platelets
5. Fibrinogen;
6. Fibrin degradation
products or D-dimer;
7. Antithrombin III.