Nabiha H Saifee

Background Direct oral anticoagulants (DOACs) and fondaparinux with stable pharmacokinetics are commonly used anticoagulants for outpatient care. Due to the lack of monitoring requirements, drug-specific assays are not available in most hospital laboratories, but drug levels are needed in some urgent/emergency situations. This study describes the development of a qualitative screen for the presence of DOAC or fondaparinux using coagulation tests found in most laboratories. Methods The DOAC screen is composed of a heparin anti-Xa activity assay and thrombin time (TT) assay. The STA®-Liquid-Anti-Xa assay calibrated with Stago Multi Hep® and STA®-TT were run on STA-R Max® analyzers. The anti-Xa activity and TT assays were repeated 5 times in samples of commercially available calibrators and controls for each drug: fondaparinux, dabigatran, rivaroxaban, apixaban, and edoxaban. Statistical analysis and correlations were performed for anti-Xa activity and TT results for each drug and pooled normal plasma. Results A significant correlation was found between heparin-calibrated anti-Xa levels and fondaparinux, rivaroxaban, apixiban, and edoxaban (r2 = 0.99–1.0). Dabigatran showed a strong linear correlation (r2 = 0.99) with TT. Anti-Xa levels >0.3 IU/mL and TT >25 seconds were determined as cutoffs at our lab for the detection of clinically relevant drug levels of factor Xa inhibitor and direct thrombin inhibitor, respectively. Conclusions Our study demonstrates that commonly available heparin anti-Xa activity and TT assays can be used to qualitatively detect DOACs and fondaparinux and provides a method to establish a qualitative interpretation.