Our January, 2021 Quick Question asked, “How does your facility monitor warfarin in an atrial fibrillation [AFIB] patient with lupus anticoagulant [LAC]? The answers were…
- PT–INR; it is valid in LAC [33%]
- Chromogenic factor X [10, CFX] [33%]
- Chromogenic anti-factor Xa [23%]
- None: we switch to a DOAC [11%]
Our question attracted too small a sample to draw conclusions, however answer 1, “PT–INR; it is valid in LAC” was the answer that we anticipated would draw the most choices because many prothrombin time reagents are relatively unaffected by LAC. While several publications have recommended CFX as an alternative assay for warfarin effects, the assay has been generally confined to reference laboratories. The chromogenic anti-Xa measures unfractionated heparin, low molecular weight heparin, and may be modified to assay direct oral anticoagulants [DOACs] apixaban and rivaroxaban, but not factor X levels. Finally, clinical studies have so far not supported acceptable efficacy and safety DOAC outcomes.