Benedict's test : The Basic Sugar Test

This is a biochemical test to detect reducing sugars in solution, devised by the US chemist S. R. Benedict (1884-1936). Benedict’s test can also be called as copper reduction; clinitest-tablet test; clinistix; diastix; tes-tape.

This comes under the urine sugars, ketones and mucopolysaccharides tests category and under subcategory of carbohydrate and fat-metabolism tests. Generally it does not the take more than 3-5 minutes for the test to be completed. This test is performed to monitor urine-sugar levels during insulin treatment and to detect excess urine-sugar levels.

All monosaccharides are reducing sugars; they all have a free reactive carbonyl group. Some disaccharides have exposed carbonyl groups and are also reducing sugars. Other disaccharides such as sucrose are non-reducing sugars and will not react with Benedict's solution. Starches are also non-reducing sugars.

Benedict's reagent consists of a mixture of copper (II) sulphate and a filtered mixture of hydrated sodium citrate and hydrated sodium carbonate and is added to the test solution and boiled. The copper sulfate (CuSO4) present in Benedict's solution reacts with electrons from the aldehyde or ketone group of the reducing sugar to form cuprous oxide (Cu2O). A high concentration of reducing sugars induces the formation of a red precipitate; a lower concentration produces a yellow precipitate. Benedict's test is a more sensitive alternative to Fehling's test.

This test is performed in a commercial laboratory, hospital, or in a doctor's office by a lab technician, nurse, doctor.

Clinitest is a self testing method to know the presence of sugars in the urine. The Clinitest Reagent Tablets contain copper sulfate, which reacts with reducing substances in urine converting cupric sulfate to cuprous oxide. This results in a color, which varies with the amount of reducing substances present. The Clinitest Reagent Tablet reacts with all reducing sugars and is not specific for glucose. Therefore, it is important to test urine from small children, under 3 years old for galactosemia. Children with galactosemia lack the enzyme necessary to convert galactose to glucose. Patients with galactosemia will test positive for Clinitest and negative for glucose using a reagent strip that is specific for glucose.

Steps to be taken care of

• Be sure hands are dry when handling the Clinitest tablets.
• Avoid contact of Clinitest tablets with eyes, mucous membranes, gastrointestinal tract and clothing because sodium hydroxide and moisture produce caustic burns.
• Keep tablets in a well-marked, childproof bottle.
• Do not use any dark-blue tablets. The normal color of fresh tablets is light blue, with darker-blue flecks.
• During the bubbling action, hold the test tube near the top to avoid burning your hand. The tube becomes boiling hot.

Preparing for the Test

There is no change of activity or change of diet required for this test. Patients should inform the person performing the test if they have recently taken any medications listed under Taking these drugs may affect test results. You may be asked not to take this medication before the test.

This test uses a

• Sterile urine container.
• Clinitest (commercially produced tablet).
• Clinitest color chart.
• Medicine dropper.
• Test tube.

After the test

There is no requirement for any immediate post test care. Patients should ask for written guidelines and a flow sheet to record the clinical test results and details of the insulin therapy at home.

Test results are determined by comparing results to color chart enclosed in the home test.