Comparison of a commercial modified factor VIII bethesda inhibitor assay to current factor VIII inhibitor assay methods in a multicenter trial.

Patients with hemophilia A may develop antibodies (also known as inhibitors) to factor VIII (FVIII) after exposure to treatment products. These antibodies inhibit FVIII function and interfere with treatment using FVIII replacement products. Interlaboratory variation of inhibitor assay results continue to be problematic for the management and treatment of patients with hemophilia A. A commercial FDA-cleared FVIII inhibitor kit (F8Inh Kit) has been developed to bring consistency to FVIII inhibitor assessment. The aim of this study was to compare the kit's performance to in-house methods for FVIII inhibitor quantification in 24 North American and European laboratories. We performed a comparative method study from Q4 2018 to Q1 2019. Each laboratory performed FVIII inhibitor assays on the test samples using their in-house method and using the F8Inh Kit per the validated and approved procedure outlined in the package insert. A total of 470 data sets were received, and the overall imprecision for all laboratories improved for the control mix when it was standardized using the PBI F8Inh Kit with a significant decrease in coefficient of variation relative to in-house methods. The F8Inh Kit provided a standardized method and reagent set showing significant potential for laboratories seeking to establish accurate and precise FVIII inhibitor measurements.