Lupus Anticoagulant and Factor XI

Here is a message from Carol Houde of Emerson Hospital:

I’m interested in the association between elevated factor XI activity and the lupus anticoagulant. When doing dilutions how do you effectively differentiate between the “lupus effect” on this PTT-based assay (especially when the LA result is borderline positive)?

Hi, Carol. Sorry to say, I know of no relationship between elevated factor XI and lupus anticoagulant prolongation of the PTT. I do know if you attempt a PTT-based assay of VIII, IX or XI in a lupus anticoagulant positive plasma you are likely to get a false reduction. I’m posting this question for assistance from our subscribers.