In vivo recovery of factor VIII: a comparison of one-stage and two-stage assay methods.

The recovery and half-life of VIII:C in the plasma of severely haemophilic patients was measured by one-stage and two-stage assays after injection of two Factor VIII 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 two assay methods. The one-stage assays gave the most consistent results, in that the average recovery was 100%, whereas the two-stage assays gave only about 80% of the value expected from in vitro assays. There was no differences in recoveries between the two concentrates. The two-stage assays gave a slightly shorter half-life than the one-stage assays, and the half-life of Hemofil was also shorter than that of Fraction I-O.