Urine Ketones

Authored by , Reviewed by Dr Adrian Bonsall | Last edited | Meets Patient’s editorial guidelines

Ketones are produced when the body burns fat for fuel. Normally these ketones will be completely broken down (metabolised) so that there are very few ketones in the urine. If for any reason the body cannot get enough glucose for energy it will switch to using body fats, causing an increase in ketones in the body. This results in more ketones present in the urine.

Ketones are produced when the body burns fat for energy. Normally, your body gets the energy it needs from carbohydrate in your diet. But stored fat is broken down and ketones are made if your diet does not contain enough carbohydrate to supply the body with sugar (glucose) for energy or if your body can't use blood sugar (glucose) properly.

Ketones are usually formed in the liver and are broken down so that very small amounts of ketones appear in the urine. However, when carbohydrates are unavailable (for example, in starvation) or can't to be used as an energy source (for example, in diabetes), fat becomes the main source of energy and large amounts of ketones are made. Therefore, higher levels of ketones in the urine indicate that the body is using fat as the major source of energy.

High levels of ketones in your body can cause tummy (abdominal) pain, feeling sick (nausea), being sick (vomiting) and diarrhoea. The ketones that most often appear in the urine when fats are burned for energy are called acetoacetate and beta-hydroxybutyric acid.

The causes of high levels of ketones and therefore ketones in your urine include:

  • Poorly controlled diabetes.
  • Diabetic ketoacidosis (DKA).
  • Starvation: not eating for prolonged periods (for example, 12 to 18 hours).
  • Anorexia nervosa.
  • Bulimia nervosa.
  • Alcohol dependency.
  • Ketogenic diet (high-fat, low-carbohydrate diet). This can cause an increase in body ketones but much less than DKA and not usually harmful to the body. Ketogenic diets have been used as a treatment for epilepsy.

Ketones can be tested using a blood test or a urine test. The urine test for ketones is performed using test strips. There are several reasons why a ketone test may be needed:

  • It is a convenient way to monitor diabetes in addition to monitoring blood sugar (glucose) levels, especially when the glucose levels are high and there is a risk of DKA.
  • It is also useful for people on a high-fat or low-carbohydrate diet to monitor ketone levels.

Ketone testing is also used for someone who cannot eat due to fasting or to eating disorders like anorexia. Pregnant women with diabetes should also be monitored with a ketone test.

Occasionally the urine ketone strips are positive but there aren't any ketones in the urine. The causes of this include:

  • If you are taking some medicines - for example, levodopa, sodium valproate.
  • If you are taking vitamin C.
  • If your body is very dry (dehydration).

One of the main problems with urine testing for ketones is that there is a delay in the urine becoming positive to ketones. You may have a sudden increase in the level of ketones in your blood but there will be a delay in detecting the high level of ketones in your urine.

Equally your urine may also be positive to ketones because ketones have passed into your urine over the previous few hours, even though your blood ketone levels have already started to fall.

On other occasions the urine ketone strips may be negative when there are actually ketones in the urine. Most urine testing kits detect acetoacetate, not the main ketone, which is beta-hydroxybutyrate. It is possible for the test to be negative with high levels of beta-hydroxybutyrate.

Severe insulin deficiency causes an increase in blood sugar (glucose) levels (hyperglycaemia) and a very high level of ketones in the blood and urine (ketoacidosis). Urine is tested for ketones as part of monitoring of type 1 diabetes mellitus.

Monitoring of ketones is important in all people with diabetes:

If you have diabetes and there is a high level of ketones in your urine then you should contact your GP or diabetes team immediately. If you feel very unwell or a urine ketone test result is more than 2+ then there's a high chance you have DKA, requiring emergency medical care and treatment in hospital immediately.

Diabetic ketoacidosis

DKA is a serious problem that can occur in people with diabetes if their body starts to run out of insulin. This causes ketones to build up in the body, which can be life-threatening if not spotted and treated quickly. DKA mainly affects people with type 1 diabetes but can sometimes occur in people with type 2 diabetes.

If you have diabetes, it's important to be aware of the risk and know what to do if DKA occurs. Symptoms of DKA include:

  • Needing to pass more urine than usual.
  • Feeling very thirsty.
  • Feeling sick (nausea) and being sick (vomiting).
  • Tummy (abdominal) pain.
  • Your breath smelling fruity (like pear drop sweets).
  • Your breathing becoming fast and deep.
  • Feeling very tired and confused and as though you may collapse.

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Further reading and references

  • Mitchell R, Thomas SD, Langlois NE; How sensitive and specific is urinalysis 'dipstick' testing for detection of hyperglycaemia and ketosis? An audit of findings from coronial autopsies. Pathology. 2013 Oct45(6):587-90. doi: 10.1097/PAT.0b013e3283650b93.

  • Arora S, Henderson SO, Long T, et al; Diagnostic accuracy of point-of-care testing for diabetic ketoacidosis at emergency-department triage: {beta}-hydroxybutyrate versus the urine dipstick. Diabetes Care. 2011 Apr34(4):852-4. doi: 10.2337/dc10-1844. Epub 2011 Feb 9.

  • Diabetic Ketoacidosis (DKA); Diabetes UK