Use

The quantitative measurement of rivaroxaban (Xarelto®) via a chromogenic anti‑Xa assay can be useful in clinical situations including suspected accumulation (eg, elderly patients with renal insufficiency), overdose, acute or severe renal failure and dialysis dependence, bleeding complications or thrombosis during treatment, and emergency situations such as prior to urgent surgery or life‑threatening bleeding. It may also be considered in cases of significant potential drug interaction or in patients with high BMI (>40 kg/m2) to ensure plasma concentrations fall within expected ranges. No established therapeutic ranges exist, and rivaroxaban measurement is not recommended to confirm absence of drug before invasive procedures; other assays such as thrombin time and anti‑Xa activity may be preferable. The lower limit of detection is 30 µg/L, and trough levels may fall below this threshold. Peak levels are typically sampled 3–4 hours post‑dose. Potential assay interference includes other anti‑Xa anticoagulants (unfractionated heparin, LMWH, fondaparinux), gross lipemia, hemolysis (>375 mg/dL), and icterus. Rivaroxaban can also prolong PT/INR and aPTT and interfere with many coagulation assays (Factors II, V, VII, VIII, IX, XI, XII, protein C/S activities, lupus anticoagulant), though certain assays (antithrombin III, activated protein C resistance, fibrinogen activity, thrombin time, reptilase) are not affected.