Hemophilia B with associated factor VII deficiency: a distinct variant of hemophilia B with low factor VII activity and normal factor VII antigen.

Factor VII activity and cross-reacting material was assayed in fresh and deep frozen non-contacted plasma in 43 patients with Hemophilia B belonging to different kindreds. Factor VII activity was found to be slightly decreased (about of 50% normal) in 12 patients, regardless of the thromboplastin used. In an additional patient (hemophilia BM) factor VII was slightly decreased in 1 : 10 diluted plasma but was normal in further diluted plasma. In the remaining 30 patients factor VII activity was normal. No significant variation was found between fresh and deep frozen plasmas. Factor VII antigen or cross-reacting material was normal.