Ketone Tests

Ketone Tests

Summary

Ketone tests measure the amount of a waste product called ketones in a urine or blood sample. The tests are important tools in the management of diabetes because they can detect ketosis (elevated ketone levels) and diabetic ketoacidosis, a potentially life-threatening condition.

Ketones are chemicals that are produced when the body uses stored fat instead of glucose (blood sugar) for energy. When high amounts of ketones are combined with high glucose (hyperglycemia), a person with diabetes can slip into a diabetic coma or die.

Ketone tests are especially important for people with type 1 diabetes, diabetic women who are pregnant and diabetic individuals experiencing an illness.  People with diabetes should always have a fresh supply of ketone test strips on hand for times when they suspect their ketone levels are rising.

To prevent complications, patients should discuss ketones with their physician and prepare a treatment plan in advance. Diabetic individuals with a large amount of ketones should contact their physician immediately.

About ketone tests

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.

Types and differences of ketone tests

The most common form ofketone test is a home urine test. Available without a prescription, urine ketone tests allow people with diabetes to measure their ketones with a sample of urine. People can also test their ketone levels with a blood sample. Some newer glucose meters measure ketones in addition to glucose (blood sugar).

Testing ketones in a blood sample is considered more accurate than urine testing and may be preferred by some patients because of convenience.  The ability to test with a finger prick eliminates the need to find a bathroom for urine testing. Ketones are also detectable in the blood earlier than in the urine. As a result, a patient may test positive for ketones earlier with a blood test than a urine test. The patient would then be able to treat the ketosis earlier.

Another drawback to urine strips is that they can detect only some of the ketones produced by the body. Ketones consist of acetone, acetoacetic acid and beta-hydroxybutyric acid. Only a blood test can detect beta-hydroxybutyric acid. Therefore, a urine test that does not detect any ketones may be inaccurate because it may be missing the presence of beta-hydroxybutyric acid.

Home urine ketone tests also require the user to compare a test strip to a color chart to read results. The use of a color chart introduces a number of potential problems. Patients must be able to see subtle changes in color to use a urine ketone test, which may not be possible for someone who is colorblind or whose vision is impaired by diabetic retinopathy, glaucoma, cataracts or other eye diseases. A glucose meter does not use colors. Patients also risk comparing the test strip to the chart before it has finished changing color. This can result in inaccurate readings.

Although blood tests for ketones have many advantages, they are more expensive than urine tests. Urine testing requires only disposable test strips. Blood testing requires patients to buy a glucose meter that is capable of measuring ketones, and compatible test strips that are more expensive than urine test strips.

Some physicians may prefer their patients to test their blood for ketones with a glucose meter or they may recommend testing blood in addition to using urine tests. Patients should discuss ketone tests with their physician and ask which method is best for them.

Ketone tests may also be performed in a hospital in order to diagnose ketoacidosis. The test may be conducted on a blood sample from a vein (venipuncture) or on a urine sample.

Before, during and after the ketone test

Ketone tests do not normally require preparation ahead of time. With the exception of pregnant women who test every morning, people with diabetes will usually need to test spontaneously whenever they feel ill or stressed, have very high glucose (blood sugar) levels or experience the symptoms of diabetic ketoacidosis. For this reason, patients should have a fresh supply of test strips on hand at all times.

Although the test is usually not prepared for in advance, patients should be aware that certain factors may alter test results. Diets low in carbohydrates and high in fat may affect ketone levels. Certain drugs, including corticosteroids (anti-inflammatory immunosuppressives used to treat asthma and other conditions), phenazopyridine (urinary tract pain), valproic acid (seizures), captopril (an ACE inhibitor) and levodopa (drug for Parkinson’s disease that is no longer available in the United States), may cause false-positive results.

Though dehydration is not an issue with blood testing, it may concentrate ketones in the urine and cause false results in a ketone urine test. High levels of vitamin C can cause the urine to become very acidic and cause false-negative results.

People conducting ketone tests should refer to package instructions to learn what additional factors can alter test results.

A urine ketone test involves only normal urination, and there is no discomfort. Home urine tests require patients to follow package directions carefully. Improperly storing, handling or using test strips can cause inaccurate test results. Patients should be sure the test strip has not expired.

Most urine tests require the patient to dip a chemically coated test strip in a cup of urine or pass a test strip through a stream of urine. The user then removes excess urine from the strip by gently shaking it or blotting it with a clean tissue or paper towel. After waiting the required amount of time for the test pad to change color, the user compares the color on the test strip to a color chart on the side of the test-strip vial. Patients then record their results. Urine tests performed in a hospital to diagnose ketoacidosis essentially follow the same steps.

Patients testing a blood sample with a glucose meter will have a different approach. As with urine testing, patients need to follow package directions carefully to ensure accurate results. Users insert a test strip into the meter after checking that the strip has not expired. They then use a lancet to obtain a drop of blood from a fingertip. The user applies the blood drop to the test strip and waits the required amount of time for the meter to display the test results. Patients should review testing techniques with their physician or diabetes educator to ensure that they are performing the test properly.

When a ketone blood test is performed in a hospital to diagnose ketoacidosis, blood is usually drawn from a vein (venipuncture) from the inside of the elbow or the back of the hand. First, the puncture site is sterilized with antiseptic, and an elastic band is wrapped around the patient’s upper arm. As a result, the pressure restricts blood flow through the vein and causes the veins below the band to fill with blood.

A needle is then inserted into a vein. Occasionally more than one puncture is necessary to locate a vein. Some people may feel some discomfort when the needle is inserted, but most feel only a prick or stinging sensation. Once the needle is inserted into a vein, a tube is attached to collect the blood as it begins to flow out. The elastic band is then removed.

After the necessary amount of blood is collected, the needle is withdrawn and a small cotton ball or pad is applied with light pressure over the puncture site.

Understanding ketone test results

After the blood test or urine test has been performed, the test results will be compared to a range of values. Urine ketone test results are revealed through color changes on the test strip. The amount of ketones present in the urine is expressed either quantitatively as milligrams per deciliter (mg/dL) or in descriptive terms, such as negative, trace, small, moderate or large.

Most urine ketone test values can be read as:

Test resultValue
NegativeNormal
Trace/Small< 20 mg/dL
Moderate30 to 40 mg/dL
Large> 80 mg/dL


Blood ketone test results are expressed on the glucose meter as millimoles per liter (mmol/L). Most blood ketone test values can be read as:

Test resultValue
< 0.6 mmol/LNormal
0.6 to 1.5 mmol/LSmall
> 1.5 mmol/LModerate or Large


To be prepared, patients should discuss ketone testing with their physician ahead of time. A physician can recommend what actions to take for different ketone levels.

A trace or small amount of ketones may mean that ketones are beginning to build up (ketosis). These waste products should not be allowed to build up because high amounts of ketones can lead to diabetic coma and possibly be life-threatening. People with diabetes should drink a large amount of water and, if previously recommended by a physician, take an extra dose of insulin. The patient should perform blood tests for glucose every three to four hours, checking for ketones if glucose is over their physician-recommended range (usually over 240 mg/dL for type 1 diabetes and over 300 mg/dL for other forms of diabetes).

n a person with diabetes, moderate or high amounts of ketones may be a sign of uncontrolled glucose. High ketone levels may not be a concern when glucose is within a normal range, such as with nondiabetic people trying to lose weight. However, a combination of high ketones and high glucose (hyperglycemia) can lead to diabetic ketoacidosis. Moderate or large amounts of ketones may also be found when a person is starving, has anorexia, is on a low-carbohydrate diet or has alcoholic ketoacidosis.

People with diabetes may find moderate or high amounts of ketones when they do not have enough insulin to use glucose for energy or when they have not had enough food. Patients who have a moderate or large amount of ketones should check their glucose level and call their physician immediately. The physician can recommend the actions needed to lower the ketone levels and prevent diabetic ketoacidosis. The patient may need to take an extra dose of insulin and drink water to avoid dehydration and flush out the ketones. People are advised to refrain from exercise when they have high levels of ketones and high levels of glucose. Additional glucose and ketone tests may also be required.

By recognizing the warning signs and following the physician-recommended steps, most people can prevent ketones from reaching dangerous levels. When ketones do reach dangerous levels, patients must receive immediate emergency treatment in a hospital. Patients with diabetic ketoacidosis are normally treated with an intravenous (I.V.) drip of insulin and fluids.

Patients who detect any amount of ketones should always record the test results. The results should be discussed with a physician on the patient’s next scheduled diabetes appointment.

Questions for your doctor on ketone tests

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about ketone tests:

  1. How often should I have a ketone test?
  2. Under what circumstances should I check my ketones more often?
  3. Do you recommend a ketone blood test or a urine test for me?
  4. Do you recommend a particular type of home ketone test for me? Do you recommend I use a particular glucose meter that checks ketone levels?
  5. What is my target ketone level? What do my test results indicate?
  6. Am I at high risk of ketosis or diabetic ketoacidosis?
  7. Is it OK for me to have an above-normal amount of ketones without hyperglycemia – for example, if I’m trying to eat fewer carbohydrates – or can this ketosis be risky for me?
  8. At what point do my ketone levels indicate I need to take action? At what point do they indicate an emergency?
  9. What should I do if my ketone levels are excessive?
  10. Should I regularly have any other waste product tests?
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