Our April, 2020 Quick Question was: "How does your facility measure factor VIII during HEMLIBRA therapy?" Here are our answers from 29 respondents:
a. One-stage PTT-based FVIII
assay: 17% (5)
b. Two-stage chromogenic FVIII assay: 45% (13)
c. PTT-based assay calibrated to emicizumab: 10% (3)
d. There is no reliable assay: 28% (8)
Dr. Ali Sadeghi-Khomami's comment, appended to the April 1 question, gave away the preferred answer, but here are a few comments:
a. The PTT-based one stage clot-based assay does not work, as the emicizumab (HEMLIBRA) normalizes the PTT.
b. Several companies offer newly-developed two-stage chromogenic substrate assays specific for factor VIII activity in the presence of emicizumab.
c. This answer relates to the method for measuring emicizumab activity, not factor VIII.
d. The two-stage chromogenic factor VIII assay is reliable.