In Vivo Recovery of Factor VIII: A Comparison of One-Stage and Two-Stage Assay Methods

Abstract

The recovery and half-life of factor [F] VIII:C [factor VIII clothing activity] in plasma of severely hemophilic patients was measured by 1- and 2-stage assays after injection of 2 FVIII concentrates (Hemofil, Hyland and Fraction I-O, Kabi). Plasma volumes were measured with an Evans'' Blue technique, and both concentrates and post-infusion samples were measured against the same plasma standard. There was a highly significant difference in recoveries estimated by the 2 assay methods. The 1-stage assays gave the most consistent results, in that the average recovery was 100%, whereas the 2-stage assays gave only about 80% of the value expected from in vitro assays. There was no difference in recoveries between the 2 concentrates. The 2-stage assays gave a slightly shorter half-life than the 1-stage assays, and the half-life of Hemofil was shorter than that of Fraction I-O.