Key investigations

Key investigations for apixaban and rivaroxaban poisonings include:

• coagulation assays—standard coagulation assays do not correlate with bleeding risk and are not used for monitoring in therapeutic use, but are expected to be abnormal in the context of poisoning. Any abnormality in coagulation profile should be interpreted as ongoing presence of the active drug
• anti-Xa assay—assays are available to quantify drug concentrations for apixaban and rivaroxaban. When requesting an assay, it is critical to identify the specific drug for which anti-Xa activity is to be quantified (eg a 'rivaroxaban level' or 'apixaban level'). No toxicokinetic data exist to guide interpretation of these levels and they are not independent triggers for treatment, but may be useful in monitoring response to therapy or as discharge criteria
• haemoglobin concentration—a drop of more than 20 g/L in the patient’s serial haemoglobin concentrations suggests clinically significant haemorrhage
• platelet count—thrombocytopenia (platelet count less than 50 x 10⁹/L) may further increase the risk of haemorrhage
• serum creatinine concentration—kidney impairment reduces drug clearance and increases the duration of drug effect.