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How Long Do You Wait to do LA Testing?

From someone at Lancaster General: I was wondering whether you could help me with a problem that I have not been able to resolve with certainty. It relates to how long does a patient need to be off warfarin or heparin before lupus anticoagulant testing can be done. I have seen different recommendations ranging from 2–4 weeks for the warfarin. I have not been able to find a recommendation from a panel or consensus report. Maybe I am just missing this but I would appreciate your help with your suggestions as to what you follow in your setting and what recommendations that you may give. Thank you very much for your assistance.

Hello, thank you for what turns out to be a challenging question. Based upon the vitamin K-dependent factor with the longest half-life, prothrombin at 60 hours, I suggest to wait ten days, representing four prothrombin half-lives (240 hours). By ten days the prothrombin time and partial thromboplastin time should no longer be affected by heparin or warfarin and the lupus anticoagulant profile should be valid. This concept was confirmed by frequent contributor Dave McGlasson, who first checked it with Dr. John Olson at the University of Texas Medical Center in San Antonio. However, neither Dr. Olson, Dave, nor I know of a reference documenting actual vitamin K factors’ return to normal levels after discontinuing warfarin. Heparin is of little concern, as it disappears within 48 hours. Fondaparinux (Arixtra) has a half-life of 17 hours and should be gone in three days.

Dave had a novel suggestion: assay factor X, which has the second-longest half-life, 30 hours, and when normal, proceed. Again, an appealing, but undocumented approach.

If you want to do a complete thrombophilia workup, which includes protein C and protein S, the effect of warfarin on protein S may last up to six weeks according to Heit J. Thrombophilia: Clinical and Laboratory Assessment and Management. In Kitchens CS, Alving BA, Kessler CM. Consultative Hemostasis and Thrombosis 2nd Edition, Elsevier, 2007. It is also necessary to wait at least six weeks after the resolution of a thrombotic event to ensure all coagulation and control factors have returned to baseline. Again, there is little documented experimental evidence for these time frames, they are primarily based on knowledge of the physiology of the coagulation factors. Geo.

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