Laboratory Challenges in the Era of Novel Hemophilia Therapies

The therapeutic landscape of hemophilia A and B has expanded rapidly over the past decade, encompassing extended half-life (EHL) factor concentrates, non-factor replacement therapies, gene therapies, and rebalancing strategies. While these innovations have substantially improved bleeding control, they have also introduced significant challenges for laboratory diagnostics with respect to treatment monitoring. Traditional coagulation assays, primarily one-stage clotting assays and chromogenic substrate assays, were developed for native coagulation factors and often show assay-dependent discrepancies when applied to modified factor molecules or transgene-derived factors. Non-factor therapies, including FVIII-mimetic antibodies and rebalancing agents targeting antithrombin or tissue factor pathway inhibitor, further complicate laboratory assessment, as they profoundly interfere with conventional clot-based assays or cannot be quantified directly using routine methods. In these settings, alternative analytical approaches are required. In parallel, the detection and characterization of anti-drug antibodies remain essential but analytically demanding, often relying on non-standardized methods available only in specialized laboratories. Against this background, global hemostatic assays, particularly thrombin generation assays, are gaining increasing attention as integrative tools to assess overall coagulation potential across diverse therapeutic modalities. However, methodological heterogeneity, limited standardization, and incomplete clinical validation currently restrict their routine diagnostic application. This review summarizes the laboratory challenges associated with novel hemophilia therapies, highlights assay-specific limitations and interferences and discusses emerging strategies for monitoring modern hemophilia therapies.