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Hemophilia B and Extended Half-life Concentrates

Here is another note from Paul Riley, PhD examining the effects of extended half-life factor IX concentrates. on hemophilia B testing.

Hemophilia B1:  Therapy Classes and Monitoring

Factor IX Inhibitor? Y/N Y/N
Prophylaxis Conventional half-life recombinant or plasma-derived FIX Extended half-life FIX
Preferred assay to measure FIX activity OSA2 (or CSA) CSA (or OSA)

1. Discrepancies between once-stage clot-based assay (OSA) and chromogenic substrate assay (CSA) have been reported for FIX mutations that are associated with nonsevere hemophilia B and may hinder accurate identification of patients for therapy.
2. Use of OSA depends on therapy and OSA activator.


Comments (1)
Bleeding Disorders
Oct 16, 2018 1:06pm

Again, thanks to both you and
Again, thanks to both you and Paul for bringing this forward. Having recently been in contact with Canadian HTCs that are trying to get ready for the availability of a specific extended half-life FIX product, I can tell you that the laboratory challenges of testing for some of these products are significant. As Paul points out, not all OSAs are equal in this case. In fact, the OSA reagents are not the typical ones that labs might be familiar with. That means bringing up a new test, which may require local validation. It also means a need for access to samples with the therapeutic agent included. Hopefully we can all work together to elevate the awareness with respect to the challenges associated with measuring these new treatments.

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