De novo smoldering paroxysmal nocturnal hemoglobinuria: a flow cytometric diagnosis.

An asymptomatic 26-year-old woman with mild macrocytic anemia (11.6 g Hb/dl) was studied. All biochemical parameters, bone marrow histology and cytogenetics were normal. The Ham's and sucrose tests were negative. A flow cytometric analysis revealed that CD55 and CD59 staining was absent in 20% and 21% of the granulocytes, but erythrocytes and CD34-positive bone marrow cells were CD55 and CD59 positive. Seven months after the initial study, the patient suffered an episode of hemoglobinuria, with mild anemia, moderate thrombocytopenia and a weak positive sucrose lysis test. A new flow cytometric analysis disclosed an increased percentage of CD55 and CD59 negative granulocytes and a 25% of erythrocytes with an intermediate pattern of fluorescence after CD59 labelling. At fourteen months, a population of CD55-deficient erythrocytes was detected and the Ham's test became positive. The present report is, to our knowledge, the first case of smoldering paroxysmal nocturnal hemoglobinuria in a patient with no previous aplastic anemia, or evident pancytopenia. The diagnosis was established by flow cytometry of peripheral blood granulocytes, with apparently phenotipically normal progenitor cells in an early stage of the disease. Flow cytometry appears to be a useful tool in our knowledge of paroxysmal nocturnal hemoglobinuria evolution.