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Ham's Test (Acidified Serum Test)

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal disorder of bone marrow stem cells which gives rise to blood cells that are unusually susceptible to activated complement. It may be viewed as a myelodysplastic syndrome, in which a distinct class of membrane proteins is selectively deleted from the plasma membranes of maturing blood cells. The manifestations of PNH include intravascular hemolysis, an increased risk of venous thrombosis, and associated hypoplastic anemia.

Red blood cells in patients with PNH will hemolyze with acidified normal and acidified patient's serum, whereas normal RBC's will not hemolyze. Patients with marked spherocytosis or with the rare condition, congenital dyserthropoietic anemia, type II, (HEMPAS) may have a positive test. In HEMPAS, the patient's red cells will lyse only in acidified normal serum, and not in the patient's own acidified serum. In marked spherocytosis, lysis takes place with heat inactivated serum, whereas in PNH this is not the case.

Ham’s test is now considered to be an obsolete test. PNH is now diagnosed by  Flow Cytometry.  See Paroxysmal Nocturnal Hemoglobinuria by Flow Cytometery. 

Reference value is no hemolysis.

Specimen requirement is one 5 mL lavender top (EDTA) tube and a 10 mL plain red top tube of blood should be submitted.

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