Copper Reduction Test

The copper reduction test measures the concentration of reducing substances in the urine through the reaction of these substances with a commercially prepared tablet called Clinitest. Clinitest, which reacts to glucose and to other reducing substances (mostly sugars), has almost replaced Benedict's test.

This test is most valuable for providing the patient with overt or latent diabetes a simple, at-home method of monitoring urine sugar levels. It's sometimes used as a rapid laboratory screening tool.

Purpose

• To detect mellituria
• To monitor urine glucose levels during insulin therapy, after determination that the sugar in the urine is glucose

Patient Preparation

• Explain to the patient that this test determines urine sugar level.
• If the patient has been recently diagnosed as diabetic, teach him how to perform the Clinitest tablet test.
• Provide written guidelines and a flow sheet to help him record Clinitest results at home, if appropriate.

Equipment

Specimen container, 10-ml test tube, medicine dropper, Clinitest tablets, Clinitest color chart.

Procedure And Posttest Care

• Have the patient void; then give him a drink of water.
• Collect a second-voided urine specimen after 30 to 45 minutes.

Five-drop Clinitest tablet test

• Hold the medicine dropper vertically, and instill five drops of urine from the specimen container into the test tube.
• Rinse the dropper with water, and add 10 drops of water to the test tube.
• Add one Clinitest tablet, and observe the color change, especially during effervescence (the pass-through phase).
• Wait 15 seconds after effervescence subsides, and gently agitate the test tube.
• If color develops at the 15-second interval, read the color against the Clinitest color chart, and record the results.
• Ignore any changes that develop after 15 seconds.
• Rapid color changes (bright orange to dark brown or green-brown) in the pass-through phase in a five-drop Clinitest reaction indicate glycosuria of 2% or more. Record the results as over 2% without comparison to the color chart.

Two-drop Clinitest tablet test

• Hold the medicine dropper vertically, and instill two drops of urine into the test tube.
• Flush urine residue from the dropper with water; then add 10 drops of water to the test tube.
• Add one Clinitest tablet, and observe the color change during the pass­through phase.
• Wait 15 seconds after effervescence stops; compare the color with the appropriate color reference chart, and record results.
• In a two-drop Clinitest reaction, rapid color changes (bright orange to dark brown or green-brown) in the pass-through phase indicate glycosuria of 5% or more.

Precautions

• Instruct the patient not to contaminate the specimen with toilet tissue or stool.
• Make sure hands are dry when handling Clinitest tablets, and avoid contact with eyes, mucous membranes, GI tract, and clothing because sodium hydroxide and moisture produce caustic burns.
• Store tablets in a well-marked, child­proof bottle to prevent accidental ingestion.
• Don't use discolored tablets (dark blue). The normal color of fresh tablets is light blue, with darker blue flecks.
• During effervescence, hold the test tube near the top to avoid burning your hand; it becomes boiling hot.

Normal Findings

Normally, no glucose is present in urine.

Abnormal Findings

Interfering Factors

• Failure to use freshly voided urine or to flush urine residue from the medicine dropper
• Contamination of the specimen with toilet tissue or stool
• Failure to use whole or fresh Clinitest tablets or to keep the tablet container tightly closed to protect specimen from exposure to light or moisture
• Failure to detect the pass-through phenomenon or to use the correct reference chart for color comparison of the specimen
• Cephalosporins, nalidixic acid, and large doses of probenecid (possible false-positive)
• Tetracycline and ascorbic acid (possible false-positive or false-negative, depending on test method)
• Low renal threshold for glucose
• Presence of reducing substances other than glucose