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Updated: Jun 28, 2026
Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
The influence of von Willebrand factor on factor VIII activity measurements
S Butenas1, B Parhami-Seren, K G Mann
1Department of Biochemistry, College of Medicine, University of Vermont, Burlington, VT 05446, USA. sbutenas@uvm.edu
Background:
It has been reported by multiple laboratories that the quantitation of factor (F)VIII by activity-based assays is influenced by the method, procedure and the quality of reagents used in the assays.
Objective:
To evaluate the influence of von Willebrand factor (VWF) on FVIII activity in vitro.
Methods:
The activated partial thromboplastin time (APTT) and synthetic coagulation proteome assays were used. Citrated FVIII/VWF-depleted substrate plasma (SP) (both antigens < 0.5%) was used in all APTT assays.
Results:
The concentration of FVIII antigen in pooled plasma from healthy donors [normal plasma (NP)] was 1.5 nm. The SP reconstituted with 1.5 nm recombinant (r)FVIII clotted in 23.8 +/- 0.2 s (standard deviation). The addition of 10 microg mL(-1) VWF to the SP increased the clotting time to 28.7 +/- 0.1 s; that is, the activity of rFVIII (FVIIIc) decreased to 50%. This inhibitory effect of VWF decreased with decreasing rFVIII concentration in SP, and became negligible at rFVIII
Conclusions:
VWF has an inhibitory effect on the measurement of FVIII clotting activity. This effect depends upon the structure and formulation of the FVIII product.
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