Preparation of factor-VIII-depleted plasma with antibodies and its use for the assay of factor VIII.

Standardized factor VIII (FVIII)-deficient plasma is necessary for the clotting assay of this protein. Ethical considerations and prevalence of HIV seropositivity in hemophilia A patients have required the replacement of severe hemophilia A plasma by another specific substrate for FVIII clotting assays. FVIII-deficient plasma was prepared by immunodepletion using polyclonal anti-von-Willebrand factor (vWF) and monoclonal anti-FVIII antibodies coated to agarose beads. This plasma, deficient in both FVIII and vWF, allows the evaluation of FVIII activity with a detection limit of 1% as compared to normal plasma. This immunodepleted plasma was compared to plasma from severe hemophilia A for the FVIII determination in plasma from normal subjects, severe and mild hemophiliacs, patients with von Willebrand disease and dicoumarol-treated patients. In all cases, similar values were obtained with both reagents at various levels of FVIII, with a correlation coefficient of 0.994. Such a good correlation was also obtained for the assay of FVIII in concentrates and in plasma from hemophiliacs following infusion. This immunodeficient plasma thus represents a suitable reagent for the FVIII clotting assay and provides an accurate alternative to the use of hemophilic plasma.