Which DOACs are Xa inhibitors and monitored by anti-Xa activity?

• A. Rivaroxaban and Apixaban.
• B. Dabigatran.
• C. Warfarin.
• D. Edoxaban.

Answer: (A)

Direct oral anticoagulants fall into two groups: Xa inhibitors and a direct thrombin inhibitor. An anti-Xa activity assay measures how much factor Xa is inhibited, so it can quantify drugs that directly block Xa when a drug-specific calibration is used. Among the options, rivaroxaban and apixaban are direct Xa inhibitors for which anti-Xa–based monitoring is appropriate in labs that use the correct calibrators. Dabigatran inhibits thrombin (factor IIa), so anti-Xa assays don’t reflect its activity. Warfarin is not a DOAC at all and is monitored by the PT/INR, not anti-Xa. Edoxaban is also a Xa inhibitor, but the typical testing emphasis in this context is on rivaroxaban and apixaban for anti-Xa monitoring.