Ketone Test

In the ketone test, a routine, semiquantitative screening test, a commercially prepared product is used to measure the urine level of ketone bodies. Ketone bodies are the by-products of fat metabolism; they include acetoacetic acid, acetone, and beta-hydroxybutyric acid. Excessive amounts may appear in patients with carbohydrate dehydration, which may occur in starvation or diabetic ketoacidosis (DKA).

Commercially available tests include the Acetest tablet, Chemstrip K, Ketostix, or Keto-Diastix. Each product measures a specific ketone body. For example, Acetest measures acetone and Ketostix measures acetoacetic acid.

Purpose

• To screen for ketonuria
• To identify DKA and carbohydrate deprivation
• To distinguish between a diabetic and a nondiabetic coma
• To monitor control of diabetes mellitus, ketogenic weight reduction, and treatment of DKA

Patient preparation

• Explain to the patient that this test evaluates fat metabolism.
• If the patient is newly diagnosed with diabetes, tell him how to perform the test.

Procedure and posttest care

• Instruct the patient to void; then give him a drink of water.
• Collect a second-voided midstream specimen about 30 minutes later.

Acetest

• Lay the tablet on a piece of white paper, and place one drop of urine on the tablet.
• Compare the tablet color (white, lavender, or purple) with the color chart after 30 seconds.

Ketostix

• Dip the reagent stick into the specimen and remove it immediately.
• Compare the stick color (buff or purple) with the color chart after 15 seconds.
• Record the results as negative, small, moderate, or large amounts of ketones.

Keto-Diastix

• Dip the reagent strip into the specimen, and remove it immediately.
• Tap the edge of the strip against the container or a clean, dry surface to remove excess urine.
• Hold the strip horizontally to prevent mixing the chemicals from the two areas.
• Interpret each area of the strip separately. Compare the color of the ketone section (buff or purple) with the appropriate color chart after exactly 15 seconds; compare the color of the glucose section after 30 seconds.
• Ignore color changes that occur after the specified waiting periods.
• Record the results as negative or positive for small, moderate, or large amounts of ketones.

Precautions

• Test the specimen within 60 minutes after it is obtained, or you must refrigerate it.
• Allow refrigerated specimens to return to room temperature before testing.
• Don't use tablets or strips that have become discolored or darkened.

Normal Findings

Normally, no ketones are present in urine.

Abnormal findings

Ketonuria may occur in uncontrolled diabetes mellitus or starvation. It also occurs as a metabolic complication of total parenteral nutrition.

Interfering factors

• Failure to keep the reagent container tightly closed to prevent absorption of light or moisture or bacterial contamination of the specimen (false-negative)
• Failure to test the specimen within 1 hour or to refrigerate it
• Levodopa, phenazopyridine, and sulfobromophthalein (false-positive results when Ketostix or Keto-Diastix is used instead of Acetest)