Our June 2024 Quick Question attracted 18 responses. This month’s Question was a poll that asked, “How do you assay factor concentrates?” Here are our answers:
- Clot-based assay: 11 [61%]
- Chromogenic substrate assay: 4 [22%]
- Other: 3 [17%]
Factor assays are most often requested to monitor hemophilia factor concentrate activity for patient-specific efficacy and the presence of inhibitors. The time-honored one-stage clot-based assays (OSA) for FVIII or FIX concentrates rely on the PTT, whose formulations vary by manufacturer. The greatest variation is in the activator, be it silica, ellagic acid, kaolin, or others. The OSA has served us well for standard plasma-derived factor concentrates, However, beginning with the BDD synthetic FVIII concentrate available since 2001, the extended half-life (EHL) FVIII and FIX, 2014, the factor bypassing agents such as emicizumab, 2019; and the FVIII formulation efanesoctocog alfa (Altuviiio®, 2023) that is bound to an Fc fragment plus a VWF analog, the OSA outcomes vary by reagent formulation, instrumentation, and by the therapeutic product. Medical lab professionals must communicate with the provider about the therapeutic product’s identity and the assay reagent’s sensitivity to provide reproducible results.
Lab scientists have become more familiar with the two-stage chromogenic substrate assays (CSA) that became available in 2019. The CSA provides better reproducibility for our current therapeutic EHL FVIII and FIX concentrates and for assaying in the presence of Hemlibra®. As we develop the CSA parameters such as bovine versus human substrates, more and more facilities move to the new assays. For detailed OSA and CSA capabilities for various factor concentrates, click Chromogenic FVIII and VIX Testing, a May 8, 2024 presentation by Precision BioLogic Inc. scientists Ian Burns and Dr. Jon Geske.
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