Pyruvate kinase is a blood test to detect abnormally low levels of pyruvate kinase (PK), an enzyme that helps convert glucose to energy when oxygen is low (termed anaerobic metabolism).

PK is found in red blood cells. If the amount of PK is deficient, the red blood cells break down more rapidly than usual. This destruction can result in hemolytic anemia, or too few oxygen-carrying red blood cells.

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill 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 the laboratory, white blood cells are removed because they can alter test results, and the level of pyruvate kinase is analyzed.

If your child is to have this test performed, it may be helpful to explain how the test will feel, and even demonstrate on a doll. Explain the reason for the test. Knowing the "how and why" may reduce the anxiety your child feels.

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

Hemolytic anemia has many causes. It may be present from birth or acquired. A deficiency in pyruvate kinase is fairly rare, and this test helps your health care provider determine the cause of your anemia.

The pyruvate kinase level is measured in relation to the amount of hemoglobin (a normal part of red blood cells) in the sample. The results vary depending upon the testing method used. The laboratory performing the test should be consulted for the range of values seen in healthy individuals.

Low levels of pyruvate kinase confirm pyruvate kinase deficiency. Your health care provider can also distinguish between anemia caused by pyruvate kinase deficiency and other inherited disorders.

Risks associated with having blood drawn are slight:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

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.