The examination of urine (pyhsical, chemical and microscopic) is called Urinalysis. It provides a valuable picture of the general health pattern of a patient. Urinalysis is usually done to
(i) find out the state of the kidneys and the urinary tract, and
(ii)gather information about metabolic and systemic abnormalities.
To diagnose metabolic and systemic disorders such as diabetes and jaundice, tests for glucose, ketone bodies, bilirubin and urobilinogen should be carried out.
Urine is mainly composed of 95% water, and the rest being made of urea, uric acid, creatinine, sodium, potassium, chloride, calcium, phosphates etc. It must be collected in a clean, dry container and examined as soon as possible. For testing glucose, urine collected 2 to 3 hours after food is suitable.
Sugars are generally known as reducing substances because they can reduce a heavy metal, such as copper, from a higher to a lower oxidation state for example, the reduction of blue cupric sulphate to red cuprous oxide. Glucose, lactose, fructose, galactoese, pentoses, sucrose etc., are the reducing substances found in urine. Even though there are many reducing substances in the urine, estimation of glucose is important, as it indicates the hyperglycemic condition.
Glucose is present in trace amonts in normal urine. In the kidneys, glucose is filtered by the glomeruli and reabsorbed by the tubules. Above a certain limit the tubules cannot reabsorb all the glucose. The surplus glucose appears in urine and this condition is known as glycosuria. When glycosuria is detected and hyperglycemia (excess glucose) is estalished, the chronic disorder, diabetes mellitus is indicated. In this condition as much as 280 milli moles/ L of glucose can be found in urine. It indicates disturbances in carbohydrate, lipid and protein metabolism.
Urine glucose is tested both qualitatively and quantitatively. Benedicts test is the qualitative test to indicate the presence or absence of sugars. Different types of quantitative tests, each of them based on some principle are also employed to quantitate the urine sugar content. Some of them are Bendicts reagent method, glucose oxidase method ,o- toluidene method etc. Thin layer chromatography is considered a superior method for identification of urine sugars. Recently, digital glucometer is in usage for instantaneous determination of blood glucose levels.