Ketones - urine

Definition

A ketones urine test measures the presence or absence of ketones in the urine.

Alternative Names

Ketone bodies - urine; Urine ketones: acetone, acetoacetic acid, and beta-hydroxybutyric acid

How the test is performed

The test requires a clean-catch urine sample.

To obtain a clean-catch sample, men or boys should clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well.

As you start to urinate, allow a small amount to fall into the toilet bowl to clear the urethra of contaminants. Then, put a clean container under your urine stream and catch 1 to 2 ounces of urine. Remove the container from the urine stream. Cap and mark the container and give it to the health care provider or assistant.

For infants, thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls, the bag is placed over the labia. Diaper as usual over the secured bag.

This procedure may take a couple of attempts -- lively infants can displace the bag. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.

Urine ketones are usually measured as a "spot test" using a dipstick coated with chemicals that react with ketone bodies. The dipstick is dipped in the urine sample, and a color change indicates the presence of ketones.

How to prepare for the test

You may have to eat a special diet, and you should stop taking any drugs that may affect the test.

If the collection is being taken from an infant, you may need extra collection bags.

How the test will feel

The test involves only normal urination, and there is no discomfort.

Why the test is performed

Ketones are the end-product of rapid or excessive fatty-acid breakdown. Examples of ketones are:

• Acetoacetic acid
• Acetone
• Beta-hydroxybutyric acid

Ketones will be present in the urine when the ketones in the blood go above a certain level.

A number of hormones, including glucagon, epinephrine, and growth hormone can cause fatty acids to be released from body fat (adipose tissue) into the blood. The levels of these hormones increase in starvation, uncontrolled diabetes, and a number of other conditions.

An insulin deficiency relative to the level of glucagon is also present in persons with diabetes.

Normal Values

A negative test result is normal. When ketones are present in the urine, the results are usually listed as small, moderate, or large with these corresponding values:

Small: < 20 mg/dL

Moderate: 30 - 40 mg/dL

Large: > 80 mg/dL

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

A positive test may indicate:

• Abnormal nutritional conditions
  • Anorexia
  • Fasting
  • High protein or low carbohydrate diets
  • Starvation
• Disorders of increased metabolism
  • Acute or severe illness
  • Burns
  • Fever
  • Hyperthyroidism
  • Nursing a baby (lactation)
  • Post-surgical condition
  • Pregnancy
• Metabolic abnormalities, including uncontrolled diabetes or glycogen storage disease
• Vomiting frequently over a long period of time

What the risks are

There are no risks.

Special considerations

Special diets can change test results. For example, a diet low in carbohydrates and high in protein and fat can raise ketone levels in the blood which can then enter the urine.

Some drugs, including glucocorticoids, can cause false positive measurements.

References

Inzucchi SE, Sherwin RS. Type 1 diabetes mellitus. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 247.