Factor VIII deficient plasma for laboratory tests prepared from normal plasma and a human antibody.

Plasma from a patient factor VIII inhibitor was mixed at several low concentrations with fresh normal plasma. The factor VIII deficient plasmas obtained after a short incubation period were used as substrate plasmas in the normal one-stage factor VIII assay method. Results obtained using 0.5-1% of the inhibitor plasma in normal plasma compared favourably with those obtained using normal haemophilia A factor VIII deficient plasma provided that tests were carried out without delay. A single plasma exchange of this patient provided enough antibody to prepare more than 500 litres of factor VIII deficient plasma by simple mixing with fresh normal plasma.