Our March, 2020 Quick Question, "How does your facility measure extended half-life factor VIII concentrate therapy?" drew 24 votes, reflecting the number of laboratories serving Hemophilia and Bleeding Disorders services worldwide. Here are the answers:
A. One-stage clot-based FVIII
assay 46% 
B. Two-stage chromogenic FVIII assay 42% 
C. We don't measure, assays are unreliable 8% 
D. Alternate method, see comment 4% [1, no comment was provided]
Thanks to our respondents. It appears there is a movement towards chromogenic factor VIII and factor IX assays, reflecting their desirable accuracy and precision. Our current reference method remains the one-stage PTT-based factor VIII assay, which may be used with the caveat that the reagent's formulation affects its FVIII accuracy. PTT reagents may employ micronized silica, polyphenols, ellagic acid, or kaolin as their negatively charged particulate activators and each responds differently to the several variant forms of EHL factor VIII, which may employ Fc fusion, PEGylation, VWF , or other "chaperone proteins." While it is true that several PTT reagents may report accurate EHL FVIII results if well-matched, the advantage of the the chromogenics is that they appear to recover varios EHL FVIIIs at a predicted 100% level. Refer to the open-access article, Church N, Leong L, Katterle Y, et al. Factor VIII activity of BAY 94-9027 is accurately measured with most commonly used assays: Results from an international laboratory study. Haemophilia 2018 DOI: 10.1111/hae.13564 [click or tap here], :/sites/default/files/bay_94-9027_assays_church_hemophilia_2019.pdf
Judging by feedback from George's local Hemophilia and Bleeding Disorders of Alabama, a branch of the National Hemophilia Foundation, many hemophiliac boys are now being switched to game-changer injectable emicizumab (HEMLIBRA®), whose efficacy extends for as long as one month with relatively few safety issues. HEMLIBRA causes new laboratory challenges that lead to our April, 2020 Quick Question [click or tap]. We look forward to your April responses.