Clinical Significance

The acidity of the urine is normally influenced chiefly:

1. by the nature of the diet, i.e. alkaline or acid ash.

(a) ingestion of large amounts of proteins (meat, bread, fish etc) which yields acids in the course of metabolism (like H2SO4, phosphoric acid, etc) increases urinary acidity and NH3.

(b) Most vegetables and fruits (orange, lemon, apple, peach etc) contain organic acids, e.g. citrates, oxalates, which form HCO3- (bicarbonate) in the body making the urine alkaline and hence decrease urinary acidity.

(c) Certain other fruits like plums, cranberries, contain benzoic acid and quinic acid, which are metabolized to and excreted as hippuric acid, increasing the urinary acidity and NH3

(d) Urinary acidity and NH3 are also increased by starvation and dietary carbohydrate restriction. In these, there is increased catabolism of body proteins and fats with increased urinary excretion of SO4, PO4 and ketone bodies as OH-butyric acid and acetoacetic acid.

2.Urine should not be permitted to decompose during or after the collection of a 24-hour sample. If contamination is there, the microorganisms will start growing and they convert the urea of urine to ammonia carbonate and the urine becomes ammoniacal. To avoid this change, the urine must be kept in refrigerator temperature and a suitable preservative like thymol, toluene or conc.HCL may be added to the container before starting collection of urine.

V. Odor

Freshly voided urine in a normal healthy person or the urine which has not been permitted to spoil, has a not unpleasant odor described as aromatic odor. If urine does not have such an odor soon after it is passed it may be in a pathologic state.

Causes of abnormal odor

1. A putrid or strongly ammoniacal odor points to decomposition by bacteria, probably occurring in the urinary bladder.

2.An unpleasant odor is due to excretion of methyl mercaptan

(i) after partaking of food like asparagus

(ii)methyl mercaptan is some times formed from abnormal metabolism of aminoacid methionine in cases of hepatic failure and excreted in urine.

3. Fruity odor found when a large amount of acetone is excreted in urine in diabetic ketoacidosis. This may help in diagnosis.

4.A peculiar “mousy” odor is found in inherited disorder “phenylketonuria”, in which ‘phenyl-acetyl glutamine’ is excreted and account for the odor.

VI. Turbidity

Normal urine is almost always perfectly clear and transparent when voided. On standing, there is likely to separate out a faintly cloudy flocculation, believed to be mucoprotein or nucleoprotein, which is present only in traces, together with some epithelial cells.

Mucus

It appears as a flocculent precipitate, which gradually sinks to the bottom of the urine. Mucus occurs in greater amounts in

(i) in inflammatory conditions of urinary tracts,

(ii)after prostatic massage, or

(iii)when the urine contains semen or vaginal discharge.