This test measures the amount of ketones in the blood. Ketones are substances that are produced when fat cells break down. They can make the blood too acidic (ketoacidosis).

Any amount of detectable ketones is considered abnormal.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to cause the veins below the band to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Fast for 4 hours before the test.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is used to diagnose ketoacidosis.

A test result is positive if ketones are found in the blood. This may indicate:

• Alcoholic ketoacidosis
• Starvation
• Uncontrolled blood glucose in diabetics

The only risks are those associated with the venipuncture.

A diet low in carbohydrates can increase ketone bodies.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.