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Ham's (acid hemolysin) test   

Overview | Risks | Results

Alternative names:

Ham test

Definition:

A test to look for increased fragility of red blood cells in mild acid.

How the Test is Performed

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), 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 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

This test is used to confirm the diagnosis of PNH (paroxysmal nocturnal hemoglobinuria).

Diagnosis of PNH can be confirmed by having a positive acidified serum test (Ham test). In acidified serum, complement is activated by the alternate pathway. It binds to red blood cells, and lyses the abnormal PNH cells which are unusually susceptible to complement. With newer methods of diagnosis, such as flow cytometry, this test has become less important in the diagnosis of PNH.

The Ham test is also positive in another rare disorder called congenital dyserythropoietic anemia, but in this case the sugar-water fragility test is negative.  Furthermore, the clinical aspects of this disorder are not similar to PNH.

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