Paroxysmal Nocturnal Hemoglobinuria : The Role of Antibodies in the Diagnostic Thrombin Test

N ABNORMALITY of the red cells of paroxysmal nocturnal hemoglobinuria ( PNH ) is responsible for their short life span in the circulation anu their lysis in vitro by certain factors present in normal plasma or serum. The hemolytic system in vitro is characteristically more active when the serum is made somewhat acid, about pH 6.8. The addition of thrombin to the serum is also capable of increasing the hemolytic activity. These two phenomena, enhancement of hemolysis by acidification and by thrombin, are the basis of several diagnostic tests for the disease. Although several studies dealing with these phenomena have been published, it is not yet known how either of the tests vorks.37 Hinz recently proposed a mechanism whereby the thrombin preparations may enhance PNH hemolysis.5 He demonstrated that thrombin of bovine origin was contaminated with heterophil antibodies and that these antibodies were capable of acting as immune hemolysins to hemolyze PNH red cells independent of the PNH hemolytic system. When these antibodies were absorbed by preliminary incubation of the thrombin solutions with normal human red cells, the matonal would no longer enhance hemolysis in the thrombin test. It is known that PNH red cells are exceptionally susceptible to hemolysis by various kinds of hemolytic antibodies,#{176} and therefore it seemed reasonable to conclude that the thrombin test was positive in PNH because of the presence of the contaminating antibodies in the thrombin preparations. We found in thrombin the antibodies described by Hinz. After we had removed the antibodies, the “absorbed thrombin” was used in the thrombin test with red cells of several patients with PNH. The tests were positive in every case. This report deals with the basis of the discrepancy.