This 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, and if deficient, the red bloods cells break down more rapidly than usual. This destruction can result in hemolytic anemia, or too few oxygen-carrying red blood cells.
How the test is performed
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.
How to prepare for the test
If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.
How the test will feel
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.
Why the test is performed
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 constituent 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.
What abnormal results mean
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.
What the risks are
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.
by Dave R. Roger, M.D.