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June 2024 QQ Poll Summary: OSA and Chromogenics

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:

  1. Clot-based assay: 11 [61%]
  2. Chromogenic substrate assay: 4 [22%]
  3. 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 [OSAs] for factors VIII or IX concentrates rely on the PTT, whose formulations vary by manufacturer. The greatest variation is in the form of an 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 B-domain deleted 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 that binds a VWF analog, Altuviiio [2023], the outcomes of the OSAs vary by reagent formulation 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 over time.

Lab scientists are less familiar with the two-stage chromogenic substrate assays available since 2019. In general, the chromogenics provide better reproducibility for our current therapeutic EHL FVIII and FIX concentrates and for assaying in the presence of hemlibra. While we must understand the parameters of chromogenic assays such as the use of bovine versus human substrates, more and more facilities are moving to the new assays. For detailed information on OSA and chromogenics for various factor concentrates, click this link to a May 8, 2024 presentation by Precision BioLogic Inc. scientists Ian Burns and Dr. Jon Geske entitled Chromogenic FVIII and VIX Testing.


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