Here are the unsurprising resuts of our June, 2018 Quick Question, “How do you measure factor VIII therapy?”
- Clot-based factor assay: 82% (36)
- Immunoassay: 5% (2)
- Chromogenic substrate: 14% (6)
Dave McGlasson suggested this question because our current clot-based methods are unreliable when assaying for synthetic B-domain deleted and extended half-life preparations, many of which are also B-domain deleted. Our clot-based assays, which have always suffered from imprecision, are relatively inaccurate when measuring the newer synthetic concentrates. A number of rresearchers are now developing new, more accurate measures that we will be reporting on as they are developed.
There really aren’t many new
There really aren’t many new hemophilia therapies for which chromogenic assays are preferred. Really only emicizumab (Hemlibra), Adynovate, Afstyla, Refacto, and Idelvion fall into this category of having no effect on chromogenic assays. Before labs go down the road of validating these assays, they should inquire of their clinicians as to how many of these patients are being treated regularly at their centers. However, there are other uses of chromogenic assays, such as for situations where patients have mutations giving rise to discrepant results between clotting and chromogenic assays, or if patients have lupus anticoagulants affecting the PT and aPTT used for the clotting assay.