Antibody studies of factor VIII inhibitor in a case with Waldenström's macroglobulinemia

We report a case of Waldenström's macroglobulinemia with prominent bleeding tendency; laboratory investigation revealed an elevated activated partial thromboplastin time. Further laboratory evaluation showed circulating factor VIII anticoagulant, deemed polyclonal IgG, with a titer of 700 Bethesda Units/ml. The factor VIII inactivation kinetics of the patient plasma were identical to those of a type II inhibitor, and the inhibitor was found to recognize the A2 domain of the factor VIII heavy chain. Apparently, paraprotein is not always the cause of reduced activity of coagulation factors in neoplastic dysproteinemias.