The Effects of Indirect- and Direct-Acting Anticoagulants on Lupus Anticoagulant Assays

OBJECTIVES: To investigate the effects of indirect- and direct-acting anticoagulants on the interpretation of lupus anticoagulant (LAC) assays. METHODS: A retrospective database review was performed to identify all LAC panels from November 2012 to November 2015. The positivity rates for three LAC tests were compared among various anticoagulant medications. RESULTS: This analysis included 7,721 LAC panels. Direct oral anticoagulants, warfarin, and unfractionated heparin (UFH) were associated with higher LAC positivity rates compared with patients not receiving documented anticoagulation (83% for argatroban, 58% for dabigatran, 72% for rivaroxaban, 53% for apixaban, 56% for warfarin, and 36% for UFH vs 29% for no anticoagulation, P < .025). Direct thrombin inhibitors mainly affected the activated partial thromboplastin time-based assays and the tissue thromboplastin inhibition index (TTI), while direct factor Xa inhibitors mainly affected the TTI and the dilute Russell viper venom ratio. CONCLUSIONS: Results of LAC testing performed while patients are receiving anticoagulant therapies should be interpreted with caution to avoid misdiagnosing patients with the antiphospholipid syndrome and potentially committing them to long-term anticoagulation therapy.