The Laboratory Diagnosis of Paroxysmal Nocturnal Hemoglobinuria (PNH): Update 2010

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired stem cell disorder associated with periodic hemolytic events. This benign clonal condition is caused by the abnormal X-linked phosphatidylinositol glycan class A (PIGA) gene and has been associated with cytopenias and thrombosis. Recent improvements in PNH diagnostics relate to technical advances in flow cytometry (FCM), which can detect PNH cells at about 0.01% of total cells. Also, limitations of fluorescent inactivated aerolysin (FLAER) for measurement of the RBC clone have been recognized. Earlier methods involved immunological techniques associated with complement-mediated RBC lysis. These tests, including both Ham's acid hemolysis test (HT) and the sucrose lysis test (SLT), can detect PNH cells at <5% of total cells. These lytic techniques have been replaced by multi-color FCM with monoclonal antibodies (mAbs), such as CD 55 and CD 59, and FLAER, which both bind to the normal glycophosphatidylinositol (GPI)-anchors, or GPI-anchor proteins.