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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

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

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 can confirm 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

Abnormal results may be due to:

  • Paroxysmal nocturnal hemoglobinuria
  • Congenital dyserythropoietic anemia

What the risks are

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)

Special considerations

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

References

Elghetany M, Banki K. Erythrocytic disorders. In: McPherson R, Pincus M, eds. . 21st ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 31.

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

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    Encyclopedia content is provided as information only and not intended to replace the advice and instruction from your personal physician.