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Updated: Jun 13, 2026

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
The "normal" factor VIII concentration in plasma
Saulius Butenas1, Behnaz Parhami-Seren, Anetta Undas
1Department of Biochemistry, College of Medicine, University of Vermont, Burlington, VT 05446, USA. sbutenas@uvm.edu
Introduction:
The quantitation of factor (F)VIII by activity-based assays is influenced by the method, procedure, the quality and properties of reagents used and concentrations of other plasma proteins, including von Willebrand factor (VWF).
Objective:
To compare FVIII concentrations measured by activity-based assays with those obtained by an immunoassay and to establish the influence of plasma dilution on the FVIII clotting activity (FVIIIc).
Methods:
The APTT, a chromogenic assay (Coatest) and two in-house immunoassays were used. Albumin-free recombinant FVIII was used as the calibrator in all assays.
Results:
For a group of 44 healthy individuals (HI), the mean value observed for FVIII antigen (FVIIIag; 1.22+/-0.56 nM; S.D.) is substantially higher than that for FVIIIc (0.65+/-0.29 nM) and the chromogenic assay (FVIIIch; 0.50+/-0.23 nM). A positive correlation between FVIIIag and VWFag with R(2)=0.20 was observed. Since plasma VWF has an inhibitory effect on FVIIIc, we evaluated the influence of plasma dilutions on FVIIIc in HI (n=105). At a 4-fold dilution, estimates of FVIIIc by clotting assay were much lower than FVIIIag (0.77+/-0.31 vs. 1.14+/-0.48 nM). At 10- and 25-fold dilutions, the estimated FVIIIc increased to 0.87+/-0.36 and 0.94+/-0.44 nM, respectively.
Conclusions:
1) In plasma, FVIIIag is higher than FVIIIc and FVIIIch; and 2) Real FVIII concentrations in plasma can be estimated by measuring FVIIIag.
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