ABSTRACT
Acquired aplastic anaemia (AA) has been traditionally defined as the presence of peripheral blood pancytopenia associated with a hypocellular bone marrow in the absence of (a) an abnormal infiltrate, (b) an increase in reticulin or (c) morphological abnormalities in the remaining haemopoietic cells. Differentiation of cases of AA from hypoplastic myelodysplastic syndrome (MDS), however, may be difficult on morphological grounds. Special investigations such as cytogenetics on bone-marrow cells, clonogenic cell cultures and clonality studies may be helpful in some, but not all, cases. The association between AA and paroxysmal nocturnal haemoglobinuria (PNH) is more frequent and complex than previously realized. The routine availability of flow cytometric analysis of phosphatidylinositolglycan (PIG)-anchored proteins enables more sensitive detection of a small PNH clone not only among red cells, but also monocyte, neutrophil and lymphocyte populations [1-3]. The demonstration of a PNH clone in 2050% of patients with AA who have a negative Ham test, has implications not only for the pathogenesis of AA but also possibly for prediction of outcome following
immunosuppressive therapy and prediction of graft rejection in patients who are transplanted using additional immunosuppression in the form of monoclonal antibodies such as Campath-1G which recognizes the CD52 antigen, a PIG-anchored protein [4].
