Ketone tests are used to measure the amount of ketones, an acidic waste product, in a person’s urine or bloodstream. People without diabetes normally have only a trace amount of ketones in their blood and urine. People with diabetes, however, have an increased risk of developing an elevated level of ketones (ketosis). Left untreated, ketones can continue to build up in the blood, resulting in a life-threatening condition known as diabetic ketoacidosis.

Ketones are chemicals produced when the body uses stored fat instead of glucose (blood sugar) for energy. The body cannot tolerate large amounts of ketones because they act as a poison, and it tries to get rid of them through the urine. The body is incapable of releasing all of the ketones in this way, so they begin to build up in the blood.  

Ketosis and ketoacidosis are more common in patients with type 1 diabetes. They may result from missed doses of insulin. They may also occur in type 2 diabetes and other forms of diabetes, such as when a patient is under stress. A physician can recommend when a patient should test for ketones. Patients may be advised to test when:

• Glucose readings are too high. According to the American Diabetes Association (ADA), people with type 1 diabetes should test when their glucose level is high – typically more than 240 milligrams per deciliter (mg/dL) - or as instructed by their physician. All patients with diabetes should test when their glucose level is above 300 mg/dL. Patients with high glucose (hyperglycemia) should test for ketones every four to six hours.
  
  
• Symptoms of diabetic ketoacidosis are present. The symptoms in usual order of appearance include:
  
  
• • Increased thirst (polydipsia) or very dry mouth
  • Frequent urination (polyuria)
  • Fatigue
  • Dry or flushed skin
  • Nausea, vomiting or abdominal pain
  • Heavy, labored breathing (Kussmaul breathing)
  • Sweet, fruity-smelling or wine-smelling breath
  • Confusion
    
    
• Illness. Suffering from physical stress, such as from an illness (e.g., flu, fever, vomiting) or injury, can raise glucose levels. Patients who take insulin may have to compensate by taking more. However, ill people are less likely to eat, drink fluids and take medication. Consuming too few calories can add to the rise in ketones. Not taking enough insulin or anti-diabetic agents can add to the rise in glucose. Patients who are ill should test their ketones every four to six hours.
  
  
• Stress. Suffering from mental stress can elevate glucose. Patients under stress are also more likely to stray from their diabetes management plan by exercising less, making poor meal choices and testing their glucose less. This can add to the rise in glucose levels. People with diabetes under unusually high levels of either physical or psychological stress should test their ketones.
  
  
• Pregnancy. Diabetic women who are also pregnant are advised to test for ketones every morning whether they have type 1 diabetes, type 2 diabetes, gestational diabetes or another form of diabetes. High levels of ketones are accompanied by higher-than-normal levels of acid (acidosis). Acidosis can harm the fetus.