Ketones in urine

Ketonuria indicates the presence of ketones or ketone bodies in the urine and it is usually denoted in a urine test with a positive (+) mark.

Ketones are metabolic end products of fatty acid metabolism. When the body does not have enough glucose to use for energy, it begins to use fats as an alternative source of energy. In that case, ketones are present in the blood and in the urine.

Ketones and ketone bodies are not exactly the same thing, but they are used interchangeably in a urine test.

There are three different types of ketone bodies in the urine with the following rate:

• Acetone (a type of ketone) 2%
• Acetoacetic acid 20%
• Beta-hydroxybutyric acid 78%

Urine tests performed by reagent strips or dipsticks only detect acetone and acetoacetic acid in the urine. However, a change in the amount of acetone in the urine correlates with the same degree of change in the other ketones. For that reason, sometimes it is only measured the presence of acetone and acetoacetic acid in the urine.

The presence of ketones in the urine (ketones positive +) signifies that the body is using fat as the main source of energy because glucose is unavailable.

This is usually for the following reasons:

• Glucose is not being transported to the cells (diabetes)
• Lack of glucose in the body (due to starvation, vomiting, fasting or a high protein diet)

Ketone bodies appear in urine before there is any significant increase of ketone bodies in the blood.

Urine ketones are often monitored in patients with diabetes because it may help them to regulate the dosage of insulin to be administered.

Ketones in the urine may also be present in case of following a ketogenic diet (keto diet) with a limited carbohydrate consumption.

This test is performed along with other urine tests such as glucose in urine test. The patient must collect a sample of the urine in a specific container using a special kit. This sample will be sent to the lab for the analysis.

Ketones can be tested either with a dipstick or with a tablet that change of color in the presence of a high amount of acetone in the urine. The scale indicates small, moderate or large amounts of acetone:

• Small ketonuria: < 20 mg/dl (acetone +)
• Moderate ketonuria: between 30 and 40 mg/dl (acetone ++)
• Large ketonuria: > 80 mg/dl (acetone +++)

Symptomatic ketosis occurs at levels of about 50 mg/dl.

In laboratories, there are automated machines that perform the analysis, but it is also possible to buy strips that let you analyze a urine sample at home. They comprise up to 10 or more different reagents or chemical pads to perform different urine tests at the same time.

Normal urine should not contain enough ketones to give a positive reading for which it must be less than 5 mg/dl.

A positive result to the ketones in the urine (acetone) test may have a diabetic or nondiabetic meaning (depending also on the glucose on the urine test):

• Diabetic (usually with glycosuria)
• Type 1 diabetes
• Type 2 diabetes
• Diabetes mellitus
• Diabetic ketoacidosis
• Nondiabetic (usually in infants and in children)
• Severe stress
• Malabsorption
• Fanconi syndrome
• Acute febrile states
• Toxic states with vomiting and diarrhea
• Cachexia with vomiting
• Post-anesthesia vomiting
• Hyperemesis gravidarum
• Prolonged fasting
• Strenuous exercise

Some drugs may interfere causing a positive result for ketones in the urine:

• Levodopa
• Phenylketonuria
• Phencyclidine
• Isopropyl alcohol
• Paraldehyde
• Ether
• Phenazopyridine
• Captopril
• Antidiabetic drugs
• Phenformin
• Metformin
• Insulin