Laboratory Testing of Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs), also referred to as non-vitamin K oral anticoagulants (NOACs), have revolutionised anticoagulant therapy since their introduction in the late 2000s. These agents - dabigatran (a direct thrombin inhibitor) and the factor Xa inhibitors apixaban, edoxaban, and rivaroxaban - offer more predictable pharmacokinetics, fewer food and drug interactions, and do not typically require routine laboratory monitoring, unlike traditional anticoagulants such as warfarin and heparin. Despite these advantages, laboratory assessment of DOAC activity remains clinically important in specific circumstances, including bleeding, thrombosis during therapy, emergency surgery, renal or hepatic impairment, and suspected non-compliance.This chapter reviews the pharmacology, clinical applications, and laboratory evaluation of DOACs, outlining available assays and their principles. The gold standard for quantification is liquid chromatography-tandem mass spectrometry (LC-MS/MS), though chromogenic anti-Xa and dilute thrombin time (DTT) or ecarin-based assays are more commonly used in clinical laboratories. The impact of DOACs on routine coagulation tests such as PT, APTT, and TT is variable and reagent dependent, underscoring the need for drug-specific calibrators and assay validation.Quality assurance through both internal quality control (IQC) and external quality assessment (EQA) is essential to maintain assay accuracy and reproducibility, in accordance with ISO 15189:2022 standards. Furthermore, DOACs can interfere with other haemostasis assays - including factor assays, antithrombin, and lupus anticoagulant testing - leading to potential diagnostic errors. Recent studies demonstrate that activated charcoal-based reagents, such as DOAC Remove™ and DOAC Stop™, can effectively neutralise DOAC interference in such assays.In conclusion, while DOACs have largely supplanted warfarin in the management of non-valvular atrial fibrillation and venous thromboembolism due to their safety and convenience, laboratory testing retains a critical role in ensuring safe and effective patient management under specific clinical scenarios.