Decreased hemolytic capacity of sera form patients with paroxysmal nocturnal hemoglobinuria.

T HE ERYTHROCYTES of patients with Paroxysmal Nocturnal Hemoglobinuria (PNH) hemolyse at 37 C. in normal compatible human sera in the absence of demonstrable antibody. The reaction is complement dependent and in vivo causes a hemolytic anemia of varying severity. The diagnostic acid hemolysis test for this disorder is performed by demonstrating hemolysis of suspect erythrocytes in the patient’s serum or in serum from a serologically compatible normal subject. It is generally stated that normal serum is preferable for this test because the patient’s serum may be less hemolytic than normal.12 Moreover it has been noted that the hemolytic process in vivo is markedly accelerated by the transfusion of fresh whole blood to these patients, but the transfusion of washed normal erythrocytes ameliorates the hemolytic process. Although the washing process will remove leukocytes thereby reducing the possibility of leukoagglutinins triggering a hemolytic reaction, these data suggest that the patient’s plasma may be deficient in its hemolytic capacity, and the transfusion of fresh plasma restores the concentration of a low titer hemolytic component. Since variation in the hemolytic capacity of the plasma may be a critical factor in controlling the in vivo PNH hemolytic rate, studies were performed to determine if there is a diminution in the hemolytic capacity of the patient’s plasma.