[Paroxysmal nocturnal hemoglobinuria. Diagnosis aided by a monoclonal antibody directed against the decay accelerating factor glycoprotein].

The laboratory diagnosis of paroxysmal nocturnal haemoglobinuria (also called Marchiafava-Micheli disease) is based on the sensitivity of the patient's red cells to complement-induced lysis. In view of the clonal expression of the disease, haemolysis tests are difficult to interpret when the abnormal red cell population is small. The sensitivity of abnormal red cells to haemolysis is due to the absence of proteins attached to the cell membrane by a phosphatidyl-inositol link, which intervene in the regulation of the complement-induced lysis mechanism. Using a monoclonal antibody directed against one of these proteins, the decay accelerating factor (DAF, protein CD 55), makes it possible to diagnose paroxysmal nocturnal haemoglobinuria. DAF expression on patients' blood cells was measured by quantitative agglutination and by indirect flow cytometry. The agglutination test using polybren is a fast detection method, but it may be uninterpretable, notably in cases with positive antiglobulin (Coombs') test. In contrast, DAF expression measured by indirect flow cytometry correlates perfectly with measurement of red cell sensitivity by haemolysis tests. Using the monoclonal antibody by indirect flow cytometry is the method of choice to confirm the diagnosis of paroxysmal nocturnal haemoglobinuria and to measure the proportions of normal and abnormal red cells in case of haematological disorder.