3. Urine Ketones - Meanings and False Positive

Urine Ketones - Meanings and False Positives

This PatientPlus article is written for healthcare professionals so the language may be more technical than the condition leaflets. You may find the abbreviations list helpful.

Ketones are produced normally by the liver as part of fatty acid metabolism. In normal states these ketones will be completely metabolised so that very little, if any at all, will appear in the urine. If for any reason the body cannot get enough glucose for energy it will switch to using body fats, resulting in an increase in ketone production making them detectable in the blood and urine.

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The urine test for ketones is performed using test strips available on prescription. Strips dedicated to ketone testing include:

  • Ketostix®
  • Ketur test®
  • Combination strips such as Ketodiastix® are available but not on the NHS.

Testing should be performed according to manufacturers' instructions. The sample should be fresh and uncontaminated. Usually the result will be expressed as negative or positive (graded 1 to 4).[1] It should be noted that ketonuria is different from ketonaemia (ie presence of ketones in the blood) and often ketonuria does not indicate clinically significant ketonaemia.

Normally only small amounts of ketones are excreted daily in the urine (3-15 mg). High or increased values may be found in:

Diabetes mellitus and ketones

Metabolically severe insulin deficiency (relative or absolute) produces hyperglycaemia and ketoacidosis. Insulin lack increases release of fatty acids from adipose stores and reduces the rate of fat synthesis. Lipolysis is further increased by increased catecholamines, cortisol, growth hormone and glucagon. The free fatty acids are transported to the liver for conversion to ketone bodies, which serve as fuels for muscle and fat. Excess production of ketone bodies (aceto-acetate and beta-hydroxybutyrate) gives rise to ketoacidosis. Beta-hydroxybutyrate accounts for 75% of ketones.[2]

Urine is tested for ketones as part of monitoring of type 1 diabetes mellitus. Monitoring of ketones is important in all diabetic patients:

  • When the diet is low in carbohydrates, exercise levels are high or a combination of both.
  • In pregnant diabetics and in gestational diabetes.
  • When blood sugars are high (over 15 mmol/L).[2]
  • In DKA or with suspected ketoacidosis.

Diabetic patients who detect high levels of ketones in their urine should seek medical advice.

High-protein/low-carbohydrate methods to lose weight

There are a number of weight loss programmes now available, consisting of high-protein diets with very little or virtually no carbohydrates. The idea behind this is that, once the body realises it does not have carbohydrates for fuel, it will use protein stores initially and then fat reserves to produce energy. The breakdown of fat leads to ketones in the blood which can lead to ketosis and even ketoacidosis. Ketosis is associated with non-specific effects, such as nausea, weakness, increased sweating and lethargy. There are case reports being published highlighting the potential dangers of ketogenic diets.[3]

Ketogenic diets have also been used to control epilepsy in children but the data suggest it is for use only in selected cases and under specific conditions and guidance.[4][5]

This may occur in non-diabetic (as well as in diabetic) patients:

  • Positive test result but 'no' ketones:
    • Some medication:
      • Levodopa, for example Sinemet®
      • Phenazopyrazine
      • Valproic acid
      • Vitamin C
    • Dehydration
  • Positive result and ketones present:
    • High-fat diets (for example the Atkins Diet)
    • Some metabolic disorders and inborn errors of metabolism (ketones but low or normal blood glucose)[6]
    • Starvation (as above)
    • Poisoning
    • Ether anaesthesia
    • Alkalosis

Most urine testing kits detect aceto-acetate, not the predominant ketone beta-hydroxybutyrate. It is possible for the test to be negative with high levels of beta-hydroxybutyrate and then, as ketoacidosis improves and ketone levels fall, the urine test becomes positive (to aceto-acetate).

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Further reading & references

  1. Wilson LA; Urinalysis. Nurs Stand. 2005 May 11-17;19(35):51-4.
  2. Samuelsson U, Ludvigsson J; When should determination of ketonemia be recommended? Diabetes Technol Ther. 2002;4(5):645-50.
  3. Chen TY, Smith W, Rosenstock JL, et al; A life-threatening complication of Atkins diet. Lancet. 2006 Mar 18;367(9514):958.
  4. Coppola G, Verrotti A, Ammendola E, et al; Ketogenic diet for the treatment of catastrophic epileptic encephalopathies in childhood. Eur J Paediatr Neurol. 2009 Jul 24.
  5. Kossoff EH, Zupec-Kania BA, Rho JM; Ketogenic Diets: An Update for Child Neurologists. J Child Neurol. 2009 Jun 17.
  6. Weiner D; Paediatrics, Inborn Errors of Metabolism, eMedicine, Mar 2009
Original Author: Dr Richard Draper Current Version:
Last Checked: 11/12/2009 Document ID: 2906  Version: 21 © EMIS

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

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