How the Test is Performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. 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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

In the laboratory, white blood cells are removed because they can alter test results. The level of pyruvate kinase is then measured.

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 demonstrate on a doll. Explain the reason for the test. Knowing the "how and why" may reduce the anxiety your child feels.

How the Test Will Feel

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

Why the Test is Performed

This test is done to detect abnormally low levels of pyruvate kinase. If you do not have enough of this enzyme, red blood cells break down faster than normal. This can lead to hemolytic anemia, which is a low red blood cell count caused by an accelerated destruction of red blood cells.

See also: Pyruvate kinase deficiency (PKD)

Normal Results

Results vary depending upon the testing method used. In general, a normal value is 179 ± 16 units per 100mL of red blood cells.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Low levels confirm pyruvate kinase deficiency.

Risks

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.

Other risks associated with having blood drawn are slight but may include:

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

References

Golan DE. Hemolytic anemias: red cell membrane and metabolic defects. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 165.

Gregg X, Prchal JT. Red Blood Cell Enzymopathies. In: Hoffman R, Benz EJ, Shattil SS, et al, eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 45.

Yee DL, Bollard CM, Geaghan SM. Appendix: Normal Blood Values. In: Hoffman R, Benz EJ, Shattil SS, et al, eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 164.

Update Date: 3/21/2012

Reviewed by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; James R. Mason, MD, Oncologist, Director, Blood and Marrow Transplantation Program and Stem Cell Processing Lab, Scripps Clinic, Torrey Pines, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.