Health Encyclopedia

Ham test

Definition

The Ham test is done to diagnose paroxysmal nocturnal hemoglobinuria (PNH). The test checks whether red blood cells become more fragile when they are placed in mild acid.

Alternative Names

Acid hemolysin test

How the test is performed

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 restrict blood flow through the vein. This causes the vein 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 normal blood flow. 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 small glass tube (pipette), 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.

How to prepare for the test

There is no special preparation needed for this test.

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

A positive test confirms the diagnosis of PNH.

The Ham test can also be used to diagnose another rare disorder called congenital dyserythropoietic anemia.

Normal Values

A negative test is normal.

What abnormal results mean

Paroxysmal nocturnal hemoglobinuria
Congenital dyserythropoietic anemia (anemia associated with a hereditary problem with erythropoietin, the hormone that normally triggers red blood cell production)

What the risks are

Excessive bleeding
Fainting or feeling light-headed
Blood pooling under the skin (hematoma)
Infection
Many punctures to locate veins

Special considerations

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

References

Henry, JB. Clinical Diagnosis and Management by Laboratory Methods. 20th ed. Philadelphia, Pa: Saunders; 2001.

Review Date:4/27/2007
Reviewed By:Rita Nanda, M.D., Department of Medicine, Section of Hematology/Oncology, University of Chicago Medical Center, Chicago, IL. Review provided by VeriMed Healthcare Network.

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