False-positive lupus anticoagulant in patients receiving rivaroxaban: 24 h since the last dose are needed to exclude antiphospholipid syndrome.

Rivaroxaban, a direct factor Xa inhibitor, affects laboratory clotting tests. We report here 10 venous thromboembolism patients with false-positive lupus anticoagulant during rivaroxaban therapy. Two dilute Russell Viper Venom time (dRVVT)-based integrated assays, HemosIL dRVVT Screen/HemosIL dRVVT Confirm (Instrumentation Laboratory, LA1/LA2 (Siemens, Germany) and LA1/LA2 (Siemens, Marburg, Germany), showed that the patients were lupus anticoagulant-positive. Antiphospholipid antibodies were negative except for one patient. Screening activated partial thromboplastin time-based assay PTT lupus anticoagulant was lupus anticoagulant-positive, whereas the confirmatory Staclot lupus anticoagulant (both Diagnostica Stago, France) was lupus anticoagulant-negative. Re-examination after discontinuation of rivaroxaban (>24 h) ruled out the presence of lupus anticoagulant. Our data indicate that to reliably evaluate lupus anticoagulant in patients on rivaroxaban, blood should be drawn 24 h after the last dose.