Dabigatran tests correlate closely with dabigatran levels measured by the reference standard method, LC/MS. The dTT, ecarin tests, and the anti-IIa assay are the tests of choice to measure the plasma concentrations of dabigatran. Results must be expressed by interpolation of the clotting time or chromogenic activity from a calibration curve locally constructed by testing certified calibrators at increasing dabigatran concentrations.
When the dilute thrombin time (dTT) is used in conjunction with a drug calibrator, there is a strong linear relationship between dabigatran levels across a wide range of concentrations with less accuracy at or above 500 ng/mL.
Apixaban, Edoxaban, or Rivaroxaban tests, anti-factor Xa assays, should measure the plasma concentrations of any of these three anti-factor Xa drugs. Chromogenic assay methods allow for direct determination of the activity of the substrate. Determining anticoagulants' inhibiting activity on factor Xa is one of the most traditional chromogenic substrate methods. In this assay, activation of factor X in the sample is induced with one factor X–activating enzyme. The activated factor is directly detected with a chromogenic substrate. Undetectable anti-FXa activity probably excludes clinically relevant drug concentrations.