Lupus Anticoagulant Targets Factor XI

From Eric Creager at Diagnostica Stago:

I am curious why a strong lupus anticoagulant seems to target factor XI?. I have seen multiple cases of strong LA with a FXI assay as low as 10%. Serial dilutions sometimes show increasing FXI activity results with larger dilutions. Most recent case was a 44 YO male appearing with bleeding and a FXI of 8%. The DRVVT ratio was 1.7 ( <1.2 normal).
Is there a reason why XI becomes the target so often?

Thanks
 
Eric Creager
Central Region Support Coordinator
Diagnostica Stago Inc
Parsippany, NJ 07054

Hi, Eric. I’ve checked with a couple of colleagues, and it may have to do with the avidity of your PTT reagent for the contact factors. I’m curious about what result you got for factor XII in that last patient, and also whether substituting another reagent would make a difference. For example, if you haven’t tried it, you might want to compare one of Stago’s kaolin-based reagents with one of the silica-based. Let me know how it comes out, and also I’d like to see what some of our other technical gurus have experienced. Geo.