Qualitative Detection of Glucose in Urine

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Glucose is not present in urine, in general because in the kidneys, glucose is reabsorbed from the filtrate of glomerulus, across the tubular epithelium of proximal tubule into the bloodstream. Therefore, normal glucose range in urine is 0 mg/dL, or rarely up to 15 mg/dL. If higher than normal levels of glucose (0-15 mg/dL) is found in urine, then it can be suspected as diabetes, pregnancy, or renal glycosuria. Presence of glucose in urine was commonly tested to monitor diabetes in the past. Now, blood tests for glucose is easier than urine test. The glucose urine test may be done when there is suspect of renal glycosuria.

One of the test is based on the basis of character of glucose as it is a reducing carbohydrate because of a free aldehyde group. During the reduction process of Cu(OH)₂ to CuOH by the glucose aldehyde group, and itself is converted into a carboxyl group. CuOH and its degradation product, Cu₂O, are colored compounds. In excess of CuSO₄, the high Cu(OH)₂ content may lead to the formation of black CuO particles. This is called Trommer’s reaction and explained in the following equations;

Trommer's Explannation

Karl Trommer (1806-1879), German chemist first developed this copper reduction test in 1841, and more stable copper sulphate reagent was explained by Hermann von Fehling (1812-1885) in 1850. Even more sensitive copper reagent was described in 1908 by Stanley Benedict (1884-1936). Later, Ames (1945), the research team led by Albert & Helen Free, developed Clinitest tablet, which contained cupric sulfate, sodium hydroxide, and citric acid mixed with a bit of carbonate to make it fizz. Helen M. Free (1923-) and Alfred Free (1913–2000), revolutionized diagnostic urine testing with their invention of a chemically coated paper dipstick that measures a patient’s blood/urine sugar by changing color when dipped in a blood/urine sample.