Summary
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 difference 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.
