Techniques for demonstration of the specificity of circulating anticoagulants against antihemophilic factor (factor VIII), with studies of two cases possibly related to diphenylhydantoin therapy.

Circulating anticoagulants against antihemophilic factor (AHF, factor VIII) sometimes seem to inactivate other clotting factors as well. Measurements of the concentration of clotting factors in highly diluted plasma, or after neutralization of the anticoagulant with purified AHF, have demonstrated the specific nature of the anticoagulant in a patient under treatment with diphenylhydantoin. A second case in a patient treated with this agent, and with penicillin, an agent previously associated with the evolution of circulating anticoagulants, is also described.