The level of Factor VIII procoagulant activity (VIIIC) was found to be more than 30%
higher in heparinized plasma than in citrated plasma from the same donor when determined
by a one-stage assay (1.34 U/ml versus 1.0 U/ml). However, after Al(OH)3 adsorption
and two-stage assay, the VIIIC levels were not significantly different for the two
types of plasma (0.90 ± 0.25 U/ ml versus 0.82 ± 0.23 U/ml). If a one-stage assay
was employed after adsorption, a similar low result was obtained (0.92 ± 0.21 U/ ml
versus 0.91 ± 0.12 U/ml). This indicated that the adsorption step itself was responsible
for the difference in results. Parallel analyses of other VIII markers demonstrated
that more VIIIC antigen (VIIICAg) was removed by adsorption of heparinized rather
than citrated plasma (0.33 U/ml versus 0.12 U/ml) although there was no difference
in the level of VUI-related antigen (VIIIRAg). The results show that adsorption of
heparinized plasma prior to either one- or two-stage assay leads to a greater loss
of both VIIIC and VIIICAg activity than observed with citrated plasma and indicate
that, when applied to heparin plasma the two-stage assay for VIIIC underestimates
the actual VIIIC content.
Key words
One- and two-stage assay of VIIIC - Adsorption of heparin plasma - Al(OH)
3 effect on Factor VIII markers
