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Updated: Mar 8, 2026
Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
Development of a novel automated screening method for detection of FVIII Inhibitors
M S Evans1, K J Donaldson2, M E Eyster1
1Department of Medicine, Division of Hematology/Oncology, Penn State Health-Milton S. Hershey Medical Center, Hershey, PA, USA.
Introduction:
Factor VIII activity is routinely determined by measuring the activated partial thromboplastin time (aPTT) of a patient plasma sample and determining percent activity from a standard curve. To maximize the detection of a clotting factor inhibitor, a subjective assessment of parallelism of a patient curve compared with a standard curve is performed. We developed and validated an automated objective method to assess parallelism as a rapid screening tool for detection of an inhibitor to factor VIII during routine FVIII assays.
Methods:
We performed FVIII assays on a subset of FVIII-deficient patients with hemophilia A with and without inhibitors. Utilizing a ratio of the slopes from parallelism curves obtained by an independent Microsoft excel program in patients compared with a normal standard curve, we determined a cutoff ratio predictive for presence of an inhibitor.
Results:
A cutoff ratio of patient to control slopes of <0.45 for the detection of an inhibitor to FVIII was 100% sensitive and 91.6% specific, with a positive predictive value of 92.3% and a negative predictive value of 100%.
Conclusion:
Utilizing a ratio of the slopes from parallelism curves in patients with and without an inhibitor, we developed and validated a rapid, automated, and objective method to assess parallelism as an added screening tool for detection of an inhibitor to factor VIII during routine FVIII assays on a STAGO-based coagulation platform. This simple automated method has the potential to detect inhibitors to other clotting factors.
