Relationship of Factor VIII‐like Antigen (VIII AGN) and Clot Promoting Activity (VIII AHF) as Measured by One‐and Two‐Stage Assays in Patients with Liver Disease

S ummary . We recently observed an increase in factor‐VIII clot promoting activity as measured by a one‐stage assay (VIII AHF 1 ) in a haemophiliac with hepatitis. However, VIII AHF as measured by a two‐stage assay (VIII AHF 2 ) was 0.013 u/ml at a time when VIII AHF 1 measured 0.38 u/ml. We then studied seven non‐haemophiliacs with liver disease, and attempted to correlate the levels of VIII AHF 1 and VIII AHF 2 with factor VIII‐like antigen (VIII AGN) as measured by quantitative immunoelectrophoresis. In four of the seven patients, disproportionate elevations of VIII AHF 2 compared to VIII AHF 1 were found. Furthermore, VIII AHF 2 values correlated well with VIII AGN values. No such discrepancy was apparent in four normal control subjects. These findings emphasize the necessity for performing two‐stage assays in haemophiliacs as well as non‐haemophiliacs with liver disease to assess factor‐VIII levels. In addition, they suggest that confirmation of the diagnosis of haemophilia may not be possible in the haemophiliac with hepatitis unless VIII AHF 2 determinations are performed. The reason for the disparity between VIII AHF 1 and VIII AHF 2 levels is not apparent. However, the correlation of VIII AGN and VIII AHF 2 levels in the non‐haemophiliacs with liver disease provides further support for the concept that VIII AGN and VIII AHF are closely related or identical molecular entities.