Sep 30 2024
A 9/5/24 question from Chad Siniard, MD, director of the University of Alabama at Birmingham Hospital coagulation service, generated a discussion on the FVIII level that a facility chooses to generate an order for a Nijmegen-Bethesda FVIII inhibitor assay. Our October 2024 Quick Question (on the right} is a poll that asks, “At what FVIII activity level do you order a Bethesda inhibitor assay?” As this seems to be an open question, please select an answer and your comment below. Perhaps we can provide a useful consensus.
Comments (1)
Bleeding Disorders
Hi George, Of course there is no real correct answer to this question. In theory, 1 Bethesda Unit (BU) of inhibitor for FVIII is that capable of inhibiting 50% of the FVIII activity. Thus, it is theoretically possible to have 1 BU of inhibitor even in a patient with 100% FVIII, since their baseline level could otherwise be 200%. However, that would be a very rare event! When we did a local audit, including following patients who had acquired hemophilia A, most of the cases showing detectable inhibitors had FVIII levels of less than or equal to 15%. In our lab we will do an inhibitor screen for first presentations of FVIII of less than or equal to 20%, and progress to a full Bethesda assay if the screen confirms a FVIII inhibitor. In patients with acquired hemophilia A, we will continue to monitor inhibitor levels as requested by clinicians, and we have seen inhibitors between 1-3 BU where FVIII levels were between 30-40%.