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.