section name header

Introduction ⬇

Ketones, which result from the metabolism of fatty acid and fat, consist mainly of three substances: acetone, β-hydroxybutyric acid, and acetoacetic acid. The last two substances readily convert to acetone, in essence making acetone the main substance being tested. However, some testing products measure only acetoacetic acid.

In healthy persons, ketones are formed in the liver and are completely metabolized so that only negligible amounts appear in the urine. However, when carbohydrate metabolism is altered, an excessive amount of ketones are formed (acidosis) because fat becomes the predominant body fuel instead of carbohydrates. When the metabolic pathways of carbohydrates are disturbed, carbon fragments from fat and protein are diverted to form abnormal amounts of ketone bodies. Increased ketones in the blood lead to electrolyte imbalance, dehydration, and, if not corrected, acidosis and eventual coma.

The excess presence of ketones in the urine (ketonuria) is associated with diabetes or altered carbohydrate metabolism. Some diets that are low in carbohydrates and high in fat and protein also produce ketones in the urine. Testing for urine ketones in patients with diabetes may provide the clue to early diagnosis of ketoacidosis and diabetic coma.

Indications for ketone testing include:

  1. General: Screening for ketonuria is frequently done in hospitalized patients, presurgical patients, pregnant women, children, and persons with diabetes.

  2. Glycosuria (diabetes)

    1. Testing for ketones is indicated in any patient showing elevated urine and blood sugars.

    2. When treatment is being switched from insulin to oral hypoglycemic agents, the development of ketonuria within 24 hours after withdrawal of insulin usually indicates a poor response to the oral hypoglycemic agents.

    3. The urine of diabetic patients treated with oral hypoglycemic agents should be tested regularly for glucose and ketones because oral hypoglycemic agents, unlike insulin, do not control diabetes when acute complications such as infection develop.

    4. Ketone testing is done to differentiate between diabetic coma (positive ketones) and insulin shock (negative ketones).

  3. Acidosis

    1. Ketone testing is used to judge the severity of acidosis and to monitor the response to treatment.

    2. Urine ketone measurement frequently provides a more reliable indicator of acidosis than blood testing. It is especially useful in emergency situations.

    3. Ketones appear in the urine before there is any significant increase of ketones in the blood.

  4. Pregnancy: During pregnancy, the early detection of ketones is essential because ketoacidosis is a prominent factor that contributes to intrauterine death.

Normal Findings ⬆ ⬇

Urine: negative (<0.3 mg/dL or <0.05 mmol/L)

Serum or plasma:

Procedure ⬆ ⬇

  1. Dip the ketone reagent strip in fresh urine, tap off excess urine, time the reaction accurately, and then compare the strip with the control color chart on the container.

  2. Follow the manufacturer’s directions exactly if procedure differs from the technique just described.

  3. Do not use dipsticks to test for ketones in blood. Special testing products are designed for blood.

Clinical Implications ⬆ ⬇

  1. Ketosis and ketonuria may occur whenever increased amounts of fat are metabolized, carbohydrate intake is restricted, or the diet is rich in fats. This state can occur in the following situations:

    1. Metabolic conditions

      1. DM (diabetic acidosis)

      2. Renal glycosuria

      3. Glycogen storage disease (von Gierke disease)

    2. Dietary conditions:

      1. Starvation, fasting

      2. High-fat diets

      3. Prolonged vomiting, diarrhea

      4. Anorexia

      5. Low-carbohydrate diet

      6. Eclampsia

    3. Increased metabolic states caused by:

      1. Hyperthyroidism

      2. Fever

      3. Pregnancy or lactation

  2. In nondiabetic persons, ketonuria occurs frequently during acute illness, severe stress, or strenuous exercise. Approximately 15% of hospitalized patients have ketones in their urine even though they do not have diabetes.

  3. Children are particularly prone to developing ketonuria and ketosis.

  4. Ketonuria occurs after anesthesia (ether or chloroform).

Clinical Alert

Ketonuria signals a need for caution, rather than crisis intervention, in either a diabetic or a nondiabetic patient. However, this condition should not be taken lightly.

  1. In the diabetic patient, ketone bodies in the urine suggest that the diabetes is not adequately controlled and that adjustments of either the medication or the diet should be made promptly.

  2. In the nondiabetic patient, ketone bodies indicate a reduced carbohydrate metabolism and excessive fat metabolism.

  3. Positive urine ketones in a child younger than 2 years is a critical alert.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for urine collection, and interfering factors.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor appropriately.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Drugs that may cause a false-positive result include:

    1. Levodopa

    2. Phenothiazines

    3. Ether

    4. Insulin

    5. Isopropyl alcohol

    6. Metformin

    7. Penicillamine

    8. Phenazopyridine

    9. Captopril

  2. False-negative results occur if urine stands too long, owing to loss of ketones into the air.

  3. see Appendix E for other drugs that affect test outcomes.