Quantitative Analysis of Reducing Sugars
in Urine^12
12.1 Theory
Examination of urine for glucose is rapid and inexpensive and can be used to screen
large number of samples. The screening test detects sugars that reduce copper and
produce different shades of colors. Substances other than glucose also reduce CuSO 4
and produce positive result. Quantitative test estimates the amount of reducing
substances present in urine. This amount is sufficiently small to be detected posi-
tively with qualitative methods of glucose determination. The condition
characterized by excretion of glucose in urine is called glycosuria. The commonly
used quantitative test for urinary sugars is titration based Benedict’s test. This
method is not specific for glucose and measures all the reducing sugars present in
urine sample.
12.2 Specimen Requirement
In quantitative analysis, 24 h urine specimen is used and is preserved by adding 5 ml
glacial acetic acid (to inhibit the bacterial growth) to the container before starting the
collection. Urine should be stored at 4C during collection.
12.3 Principle........................................
Glucose or any other reducing carbohydrate reduces Benedict’s quantitative reagent
to a white precipitate of cuprous thiocyanate (instead of usual reddish brown cuprous
oxide). Besides the usual ingredient of Benedict’s qualitative reagent, quantitative
reagent contains potassium thiocyanate and potassium ferrocyanide. The disappear-
ance of the blue color and appearance of white precipitate indicates complete
reduction of copper, which is much easier to detect. Potassium ferrocyanide prevents
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_12
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