Circulating anticoagulant in a family with prolonged bleeding time and factor VIII deficiency.

A circulating anticoagulant against factor VIII activity was demonstrated in the plasma of a boy from a family with both factor VIII deficiency and prolonged bleeding time. However, the factor VIII-related antigen, ristocetin-induced platelet aggregation activity, platelet retention in glass bead columns, platelet aggregation with adenosine 5'-diphosphate, collagen and epinephrine, and clot retraction among affected members were normal. The electrophoretic mobility of factor VIII-related antigen on crossed immunoelectrophoresis was normal. The inactivation of factor VIII activity by the inhibitor was time dependent and was nonlinear as the concentration of the inhibitor was increased. Immunotyping showed that the inhibitor was IgG with k light chains.