When Do We Titer Inhibitors?

Dana Carton asks, “We currently test for factor inhibitors using the clot-based Bethesda titer as well as a chromogenic bovine assay for Hemlibra patients no matter what the factor level. We recently learned that colleagues don’t look for that inhibitor unless the factor level is less than 5%. Is this a common practice, and would there be a situation in which it would be important to test for that inhibitor no matter the level? For example in following an acquired inhibitor.”

Thanks to Dana Carton for this question. Click here for a link to a 3 February 2024 discussion of inhibitor study interpretation. and here to a 5 September 2024 post, FVIII level and Inhibitor Studies that provides a direct, though admittedly inconclusive, answer to Dana’s question. Thanks to Dr. Ali Sadeghi-Khomami for his reference to the 5 September post.

Here is a link to the open-access article that Dr. Favaloro references in his comment below: Favaloro EJ, Curnow J, Pasalic L. Laboratory assessment of factor VIII inhibitors: when is it required? A perspective informed by local practice. J Clin Med. 2024;14:13. doi: 10.3390/jcm14010013. PMID: 39797095; PMCID: PMC11720995.