Diagnosis and Classification of PNH

Abstract

PNH is an acquired stem cell disorder of a clonal nature characterized by complement-mediated intravascular hemolysis negative for the direct antiglobulin test (DAT, Coombs test), a thrombotic tendency, bone marrow dysfunction, and infrequent development of leukemia. Hemolysis and thrombosis are currently accepted as ascribable to deficiency of a series of glycosylphosphatidylinositol (GPI)-linked membrane proteins including decay-accelerating factor (DAF, CD55) and CD59 with complement-regulatory activity on blood cells. The deficiency is due to a synthetic defect of GPI caused by mutations of genes (virtually PIGA) involved in the steps of GPI biosynthesis. It has been suggested that PNH bone marrow failure is closely associated with acquired aplastic anemia, and it is considered to be immune mediated. For the diagnosis of PNH, identification of the three major clinical manifestations of hemolysis, thrombosis, and bone marrow dysfunction, as well as the detection of a simultaneous lack of multiple GPI-linked membrane proteins in individual blood cell lineages, reflecting the defect of GPI and mutations of GPI biosynthesis genes like PIGA in hematopoietic stem cells, is needed. Flow cytometry detects all blood cells lacking any GPI proteins, while conventional hemolytic tests such as the Ham’s acidified serum test (the Ham test) and the sugar-water test detect only PNH erythrocytes susceptible to autologous complement. The evaluation of hemolysis, thrombosis, and underlying bone marrow disorder virtually defines PNH classification and disease severity.