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.

Acid hemolysin test

A blood sample is needed. For information on how this is done, see: Venipuncture

There is no special preparation needed for this 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.

A positive test can confirm the diagnosis of PNH.

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

A negative test is normal.

Abnormal results may be due to:

• Paroxysmal nocturnal hemoglobinuria
• Congenital dyserythropoietic anemia

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood 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)

The Ham test is increasingly being replaced by a newer test called flow cytometry.

Elghetany M, Banki K. Erythrocytic disorders. In: McPherson R, Pincus M, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 31.

Schwartz RS. Autoimmune and intravascular hemolytic anemias In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 163.