Clinical significance of a small population of paroxysmal nocturnal hemoglobinuria-type cells in the management of bone marrow failure.

Although increased blood cell deficiency of glycosyl phosphatidylinositol-anchored membrane proteins has often been detected in patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS), the clinical significance of such paroxysmal nocturnal hemoglobinuria (PNH)-type cells remains to be elucidated. We established a sensitive flow cytometric assay capable of detecting less than 0.01% of CD59-CD55- blood cells in a sample and used the assay to examine a large number of patients with bone marrow failure. An increase in the proportion of PNH-type cells was detectable in approximately 60% of all AA patients and in 20% of all refractory anemia (RA)-MDS patients. The increase was undetectable in patients with RA with an excessive number of blasts, acute myelogenous leukemia, multiple myeloma, or systemic lupus erythematosus. Our study showed that the presence of an increased number of PNH-type cells was predictive of a good response to immunosuppressive therapy and a favorable prognosis among patients with recently diagnosed AA and RA. A sensitive flow cytometric analysis for detection of a small population of PNH-type cells in peripheral blood cells is one of the most important examinations in the management of bone marrow failure.