06 May

Glucose in Urine

Benedict’s test is the basis for Siemens (formerly Bayer) clinitest for glucose in urine.  The copper sulfate in Benedict’s reagent reacts with glucose and other reducing sugars to form a precipitate which varies in color depending upon the amount of the reducing sugar.   Benedict’s reagent is prepared with 17.3 g of copper(II) sulfate pentahydrate, 173 g of sodium citrate and 100 g of anhydrous sodium carbonate in 1 Liter of water.  Benedict’s test is performed by adding 3ml of Benedict’s solution to the urine sample and  boiling for a few minutes.  Upon cooling a precipitate will form indicating the presence of a reducing sugar such as glucose in the sample.  If the solution remains blue no reducing sugars are present.

Bayer’s Clinitest tablets contains 1 part copper sulfate, 12 parts sodium hydroxide, 4 parts sodium carbonate, 15 parts citric acid, filler and binder.  The sodium hydroxide reacts with the citric acid in solution to provide heat for the reaction.  When the tablet is in contact with the sample the solution boils and will pass rapidly through bright orange to a dark brown or greenish brown in the presence of a reducing sugar. A control solution with a known amount of  glucose should also be tested at the same time.  The color of the tube after 15 seconds is compared to a chart.  If Bayer’s Clinitest tablets are unavailable a lab may prepare their own Benedict’s reagent.   As long as a control and standard are used the test should be acceptable.


Robin Prymula