Coagulation Testing in Patients on Direct Oral Anticoagulants: Drug-Level Monitoring Necessity

Abstract

Introduction: Direct oral anticoagulants (DOACs) (dabigatran, rivaroxaban, apixaban, edoxaban) are used without routine monitoring. However, drug-level measurement may be needed for perioperative management, bleeding, or thrombosis on therapy.
Methods: Systematic review of 31 studies (n=4,102) comparing DOAC-calibrated specific assays (diluted thrombin time for dabigatran, anti-Xa for factor Xa inhibitors) versus routine coag tests (PT, aPTT). Reference standard: liquid chromatography-tandem mass spectrometry (LC-MS/MS). Outcomes: correlation coefficient (r), proportion with discordant results, clinical decision impact.
Results: Routine PT was unreliable for rivaroxaban (r=0.45) and apixaban (r=0.38). aPTT was unreliable for dabigatran at low concentrations (r=0.52). Specific assays showed excellent correlation (r>0.95). Discordance (specific assay indicating therapeutic level but LC-MS/MS showing subtherapeutic) occurred in 12% of samples due to calibration issues. Clinical management changed in 23% of cases when specific assays were used.
Discussion: DOAC-specific calibrated assays are necessary for accurate drug-level assessment. Routine coag tests are misleading.
Conclusion: DOAC-specific assays (diluted thrombin time, anti-Xa with DOAC calibrators) should be used whenever drug-level guidance is required.