acidified serum test (Ham test, acid hemolysin test)

Indications

• paroxysmal nocturnal hemoglobinuria

Clinical significance

• definitive diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) depends upon the acidified serum or Ham test
• the alternate pathway of complement is activated by acidified serum, binds to & lyses the abnormal PNH cells that are unusually sensitive to complement

Procedure

• the patients erythrocytes are saline washed, mixed with ABO-compatible serum & 0.2 M HCl
• after 1 hour of incubation, PNH cells are lysed
• the test is run in parallel using the patient's own serum along with 5 controls systematically isolating the effect of eliminating each of the reagents used, including serum with & without heat-inactivation, 0.2 N HCl & erythrocytes (normal & patient's)
• in PNH 10-50% of cells are lysed
• if lysis also occurs with heat-inactivated serum, spherocytes or antibody-sensitized cells may be responsible

Notes

• a positive Ham's test occurs in congenital dyserythropoietic anemia-2 (CDA-2 or HEM-PAS)
• however, lysis does not occur with the patient's serum & only with about 30% of normal sera
• additionally, the sucrose hemolysis test is negative in CDA-2

More general terms

• clinical hematology test

Additional terms

• paroxysmal nocturnal hemoglobinuria (PNH, Marchiafava-Micheli syndrome)