What laboratory measurements are recommended to assess residual anticoagulant activity when a patient has taken NOACs?
The thrombin time (TT) is the most sensitive test for dabigatran; even low levels of dabigatran will prolong the TT so a normal TT excludes clinically relevant dabigatran concentrations. Chromogenic anti-factor Xa assays are recommended for rivaroxaban, apixaban, and edoxaban with calibration for the specific agent. However, validation of these specialized coagulation tests is required, they are not universally available, and often have delayed turnaround time, which diminishes their usefulness in emergent situations. Asking patients when they took their last dose of NOAC is often the most practical method for quickly assessing residual anticoagulant activity.