Urine ketones: what a positive dipstick means for diabetes and beyond

When glucose cannot be used as fuel, the liver turns fat into ketones. Lab Tests Online UK explains that there are three ketone bodies: acetoacetate, acetone and beta-hydroxybutyrate, and that when fatty acids are metabolised ketones build up in the blood, causing first ketosis and then ketoacidosis, a form of metabolic acidosis most often seen with uncontrolled type 1 diabetes, which can be a medical emergency.

Excess ketones and glucose are passed into the urine by the kidneys, causing increased urination, thirst, dehydration and loss of electrolytes. This is why ketones turn up on a urine dipstick when blood levels are raised.

The NHS describes diabetic ketoacidosis (DKA) as a serious condition in which a lack of insulin causes harmful ketones to build up in the blood, which can be life threatening and needs urgent hospital treatment. Symptoms include thirst, passing urine more often, stomach pain, nausea, diarrhoea, breathing more deeply than usual, fruity breath like pear drops or nail varnish remover, tiredness, sleepiness, confusion and blurred vision, usually developing over 24 hours but sometimes faster.

It usually affects people with type 1 diabetes but can happen in people with type 2 diabetes who need insulin, and in people who have not yet been diagnosed. Causes include being unwell, injury or surgery, periods and not taking enough insulin. People with diabetes are advised to test for ketones when glucose is high and when they are ill, following their sick-day rules.

The NHS says that if you use strips to test ketones in urine, over 2+ is high, meaning you may have DKA and should call 999 or go to A&E. For blood ketones on a meter, under 0.6 mmol/L is normal, 0.6 to 1.5 is slightly high and should be rechecked in 2 hours, 1.6 to 3 means you are at risk of DKA and should speak to your diabetes care team, and over 3 is high and means you may have DKA, so call 999 or go to A&E. These are a guide: normal ketone levels can differ between people, and your own team will advise you.

Lab Tests Online UK adds that urine methods measure acetoacetate or both acetoacetate and acetone, but do not detect beta-hydroxybutyrate, the main ketone in severe DKA, and that blood testing gives a snapshot while urine shows recent rather than current ketones.

Ketosis and ketoacidosis may also be seen with starvation, alcoholism and high-fat, low-carbohydrate diets, and blood ketones may help detect ketoacidosis in people without diabetes who have symptoms, for example after drinking excessive alcohol. Ketones are also monitored in people on a ketogenic diet for epilepsy.

Use a fresh urine sample and read the strip at the time stated on the pack. Lab Tests Online UK says strips can be bought at pharmacies but are best performed by someone used to reading them. The NHS says you can get kit free from the NHS for testing blood or urine and that some glucose monitors also test blood ketones.

If you have diabetes and high ketones follow your sick-day plan, do not skip insulin even if not eating, and seek help as the NHS advises. In hospital DKA is treated with insulin, fluids and nutrients through a drip with monitoring for complications. If you do not have diabetes and have ketones on a routine dipstick, your doctor will check blood glucose and consider fasting, vomiting, alcohol or diet as causes.