Characters of urine
 |
| image credit by-Lothar Drechsel |
(1) Volume: Normal volume of urine is 0.5 to 2.5 L/day.
Obligatory urine volume : Minimum volume of urine that must be produced to excrete the solute load. It is produced in conditions of dehydration and with ful1 ADH action.
Oliguria is the condition where less amount of urine is produced which may be caused by dehydration and the volume of urine is less than 400 ml/day.
Anuria means no urine formation. Causes are urinary obstruction, severe dehydration, hypovolaemic shock, renal shutdown, etc. Clinically, anuria is said to occur when urine volume is less than 100 ml/day.
Polyuria means high volume of urine (more than 3 litre/ day). It occurs in absence of ADH, i.e., diabetes insipidus (low sp. gr., high volume). This also occurs after excessive
water intake or drinking. In diabetes mellitus polyuria occurs due to osmotic effect of sugar present in the urine (high sp. gr with high volume.).(2) Colour: Normal colour of urine is pale yellow due to presence of a pigment named urochrome. It changes in disease, e.g., yellow in jaundice.
(3) Reaction : Slightly acidic, pH 6.5, range 5 to 7.5. Urine is alkaline in post prandial alkaline tide, in hyperventilation as in high altitude or voluntary. Limiting pH is 4.5. Urine on standing, outside the body, becomes alkaline due to formation of ammonia from the urea present in it by the organism.
(4) Specific gravity: Sp. gr. of urine is highly variable and may be between 1001 to 1050, usual value is 1010 to 1025. It increases in dehydration, after a high protein diet, in glycosuria, proteinuria, etc., and decreases in diabetes insipidus (lack of ADH action) after high water intake.
Fixed sp. gr. of urine is 1010. t is found in case of chronic kidney disease, when kidney function is abnormal and urine cannot be concentrated or diluted by kidney.
Microscopic examination of Urine
This is done by examining the centrifuged deposit of urine,
Substances seen under the microscope are as follows:(a) Casts: These are solidified protein (Tamm-horsfell) substances in the shape of the renal tubules, hence called tubular casts. These may be
(i) hyaline casts (pure cast),
(i) Granular cast with fragmented epithelial cells,
(ii) RBC cast with RBC, and
(iv) WBC cast with pus cells.
Normally a few casts may be present, but the number increases in some kidney diseases. Dead leucocytes are called so. Normally
(b) Pus cells
very feW are present but increases in disease (infection). In urine of female patients, pus cell is normally more frequent. More than 10 pus cells per high power field is considered pathological.(c) Epithelial cells are also found in urine.
(d) RBCs are present in case of haematuria.
(e) Bacteria, crystals of oxalate etc. are also found.
Abnormal constituents of Urine
(1) Glucose : When present in urine in sufficient amount to be able to reduce alkaline copper sulphate solution, the condition is called glycosuria. Normally very small amount (150 mg/day) is present which cannot reduce alkaline CuSO, Glycosuria is found in diabetes mellitus (DM) due to high plasma level of sugar and also in renal disease (Renal glycosuria). There are also alimentary glycosuria (glycosuria after a large carbohydrate meal in early diabetics) and nervous glycosuria (due to high blood sugar from glycogenolysis by adrenalin). Endocrine glycosuria is caused due to increased GH, cortisol, thyroxine, etc., or due to decreased insulin.
(2) Protein: Normally trace amount (up to 150 mg) is present. When present in sufficient amount to be detected by tests (e.g., heat coagulation), it is called proteinuria. It may be due to
(a) Prerenal: cause as in multiple myeloma when excess Bence-Jones Protein is found in plasma and it comes out through urine. In pregnancy also, proteinuria can occur without kidney defect.
(b) Renal: It is due to disease in kidney, glumerulonephritis, where the negative charge of the capillary wall is probably lost, so albumin (anion) passes through easily.
(c) Post renal : Here protein is added by exudation from the inflamed urinary tract, as in urinary tract infection (UTI). Proteinuria is classified in various ways, e.g., glomerular, tubular, overflow, secretory and others.
(3) Casts : These are present in high amount in diseased condition (see microscopic examination of urine).
(4) Ketone bodies: Normally trace amount is present, but increases in diabetes mellitus and starvation. When ketosis develops. When sufficient ketone bodies are present in urine the condition is called Ketoneuria. Ketone bodies are acetone, aceto-acetic acid and B-hydroxybutyric acid.
(5) Blood: When present in small amount can be detected only by the presence of RBC in microscopic examination and it is called microscopic haematuria. It occurs in acute glomerulonephritis. Glomerular/renal haematuria is detected by dysmorphic RBC or RBC casts in urine. Excess blood may be present in urine making its colour red, then it is called frank haematuria (found in renal stone, malignancy, and in injury of the urinary tract).
(6) Bile : Normally urobilinogen is present in urine but in obstructive jaundice both bile salts and bile pigments (conjugated bilirubin) are found in urine.
(7) Etherial sulphates (Indicans) : These are the etherial sulphates of indoxyl and skatoxyl, and normally present in urine. In case of constipation these are present in high amount rendering the urine dark coloured and foul smelling. Indole and skatole are produced by bacterial degradation of proteins in stool, these compounds (indole and skatole are responsible for the foul smell of stool) are then absorbed and in the liver these are converted into indoxyl or skatoxyl which are then excreted as etherial sulphates.
(8) Hormone metabolites : Metabolites of most of the hormones are found in urine normally. These metabolites increase when there is more secretion of the hormones. One important hormone metabolite is 17 ketosteroid. It comes from the androgens and cortisol. In female, its source is adrenal cortex, but in male 2/3rd of it comes from the adrenal cortex and 1/3rd from the testes. Creatinuria means presence of creatine in urine. Normally creatine is absent in urine except in children
(9) Creatine and in pregnancy: It is found in urine in conditions of muscle Wasting (breakdown) as in starvation, thyrotoxicosis and myopathies, and in some other conditions.