Assessing Urinary Function: The Urinalysis

[Entire Lab based on Section 25.1: Physical Characteristics of Urine]

[Table 25.1: Normal Urine Characteristics]

[Table 25.2: Urine Volumes]

Urine Composition

·      Water accounts for about 95% of the volume of urine

·      The other 5% is excess vitamins, drugs, electrolytes, and nitrogenous wastes

·      Abnormal substances in the urine can be detected by urinalysis

Physical and Chemical Analysis of Urine

·      The average pH of urine is 6.0, it can range b/n 4.5 and 8.0.

·      Vegetarians have a pH above 7.0

·      High-protein diets yield an acidic pH, below 7.0

·      Concentration of urine has traditionally been measured as specific gravity. Specific gravity is a way of comparing the weight of one fluid (like urine in this case) to the weight of a reference fluid (pure, distilled water). The specific gravity of urine is between 1.003 and 1.030.

·      It is more common now for labs to measure concentration in osmolarity. The reference range for urine is around 100 – 1200 mOsmol/L.

·      Drinking lots of fluids, lowers the specific gravity (makes it more dilute). Taking in less fluids increases specific gravity (makes it more concentrated).

·      Excessively concentrated urine results in crystallization of solutes, usually salts, into insoluble kidney stones

Physical and Chemical Analysis of Urine

Certain materials in urine suggest renal disease, injury, or other pathological conditions:

·      Ketonuria (ketones in urine) – observed in the urine in the event of starvation, diabetes or a low carb diet.  Fat catabolism produces fatty acids.  The liver cells convert excess fatty acids to ketones

·      Glycosuria (glucose in urine) - indicates diabetes or stress

·      Albuminuria (albumin in urine) - suggest an increase in permeability of glomerular membrane.  May be due to injury, high blood pressure, disease, bacterial toxins

·      Hematuria (RBCs or whole blood in urine) - indicates bleeding caused by inflammation or infection of urinary tract.  Kidney stones, trauma, menstruation or tumor formation

·      Pyuria (WBCs in urine) - urinary tract infection

·      Bilirubinuria (bilirubin in urine) - result of the breakdown of hemoglobin from old RBCs being removed from the circulatory system by phagocytic cells in the liver. 

·      Urobilinogenuria (urobilinogen is produced by the breakdown of bilirubin) - may indicate hepatitis, cirrhosis, congestive heart failure, or other diseases