Laboratory measurement of the non-vitamin K antagonist oral anticoagulants: selecting the optimal assay based on drug, assay availability, and clinical indication.

Although the non-vitamin K antagonist oral anticoagulants (NOACs) do not require routine monitoring, there are special circumstances in which laboratory measurement may be warranted. The objectives of this review are to summarize evidence on the influence of the NOACs on coagulation tests and provide practical guidance to clinicians on measurement and interpretation of coagulation assays in NOAC-treated patients. Selection of an appropriate assay for NOAC measurement depends on the drug, clinical objective, and assay availability. Separate suggestions for assay selection are provided depending on whether specialized assays are available or whether choice is limited to conventional coagulation assays such as the prothrombin time (PT) and activated partial thromboplastin time (APTT). The dilute thrombin time (TT) and ecarin-based assays are able to quantify dabigatran across a broad range of concentrations, but are not widely available. A normal TT excludes clinically relevant levels. A normal APTT probably excludes excess levels of dabigatran, but does not rule out typical on-therapy drug concentrations. The PT is insufficiently sensitive to dabigatran to be useful in most situations. Factor Xa inhibitors may be quantified with an anti-Xa assay calibrated with drug-specific standards. A normal PT probably excludes excess levels of rivaroxaban and edoxaban, but not typical on-therapy levels of these agents. The PT is less sensitive to apixaban. Depending on the sensitivity of the thromboplastin reagent, a normal PT may not exclude excess levels of apixaban. The APTT has inadequate sensitivity to factor Xa inhibitors and is not recommended for their measurement.