QUALITATIVE ANALYSIS OF NORMAL URINE

 

QUALITATIVE ANALYSIS OF NORMAL URINE

 

Physical Characteristics:

 

1) APPEARANCE: Normal fresh urine is clear. Turbidity may develop on standing on the pH increases and the phosphates precipitate.

 

2) Colour: Fresh normal urine is pale yellow or amber colour. The colour may be light or dark depending on the volume. The colouring pigment is urochrome a compound of the Urobilin or Urobilnogen and a peptide of unknown structure.

 

3) Volume: The quantity of urine excreted by normal subject range from 1000-2000 ml per day. The volume is influenced by intake of fluid, protein and sodium chloride. Excessive perspiration and strenuous exercise decrease the volume of urine. A high protein diet causes a physiological oliguria due to the diuretic effect of urea formed.

 

4) Specific Gravity: The specific gravity of normal urine varies in the range of 1.012-1.024. It can be as low as 1.001 when water intake is high and as high as 1.040 when volume of urine is restricted. The specific gravity is directly proportional to the concentration of solutes excreted.

 

5) Reaction: The normal pH of the urine is ranges from 48-7.5 with an average of pH 6.0 High protein diet gives rise to a more acidic urine because more phosphates and sulphates are eliminated from the protein catabolism. Urine on standing becomes alkaline by bacterial action on urea and formation of ammonia. After meals the HCl secretion in the stomach makes the urine alkaline during the “alkaline tide”. Urine becomes slightly alkaline when the diet is rich in vegetables and fruits.

 

Chemical Constituents:

 

                Normal urine contains both inorganic and organic constituents. The inorganic constituents include Na+, K+, Ca + +, Mg + + , NH4 +, Cl-, H2PO₄, HPO^2-₄, SO^2-₄, and traces of HCO3 ions. The normal non protein nitrogenous constituents are urea, uric acid and creatinine. The total non protein nitrogen varies from 10-15 gm./day depending mainly on the protein intake. In addition to these major organic constituents detoxified products like indican and ethereal sulphates are found in urine.

 

                Since the composition of normal urine in a healthy individual varies considerably in the course of a day, for accurate analysis, it is necessary to use a 24 hours sample, the volume of which averages 1.5 to 2 litres. Since urine contains a number of organic components which are easily decomposed by bacteria, it is necessary to preserve urine samples by covering the surface with a thin layer of toluene.