June 2024 QQ: Factor Assays

Our June 2025 Quick Question is a poll that asks, “How do you assay factor concentrates?” The question reflects the current hemostasis laboratory efforts to quantify therapeutic FVIII or FIX concentrate activity given the variety of plasma-based, recombinant, B-domain-deleted, and extended half-life therapeutics. We also manage factor concentrates that are employed to control breakthrough bleeds during non-factor therapy such as emicizumab [HemLibra®]. Two approaches are available, the time-honored one-stage clotting assay and the more recently available two-stage chromogenic substrate method. Please comment below if you employ another method or if your protocol provides for using either method based on clinical needs.