From Deborah Whetzel, Children’s Hospital of the King’s Daughters, Norfolk, VA: We’ve had a couple patients lately that demonstrated inhibition but their factor VIII results are within normal limits or even elevated. The result values differ 30–40% typically between dilutions but as they’re diluted more, the values go up to 300 or 400%. FVIII values that high seem really odd to me. We dilute to 1:160, as I’ve seen recommended, with results to that point continuing to get higher. Have you seen this occur and is there something that we should be doing? Thanks for your help.
Hi, Deborah, and thank you for your question. I turned for help to a local colleague who has a lot of experience with inhibitors. She responds, “George, are they getting a positive Bethesda titer? Or is it just an inhibitor pattern in the factor dilutions? Are any other factors affected or is it just VIII? It kind of makes me think more of a lupus anticoagulant or another specific factor inhibitor. This doesn’t seem like an VIII inhibitor to me. We’ve had patients who have had inhibitor patterns due to lupus anticoagulants that have FVIIIs that high. And I can think of one patient right off hand who had a FV inhibitor who had an VIII in the 600s that had evidence of inhibition in all her factors. I hope this helps. Talk to you soon!”
I also would add, were the patients you describe bleeding? This would indicate a factor VIII inhibitor.