Andexanet alfa is indicated for adult patients treated with a direct FXa inhibitor (apixaban or rivaroxaban) when reversal of anticoagulation is needed due to life-threatening or uncontrolled bleeding. Current commercial clinical anti-FXa assay methodology yields falsely elevated anti-FXa activity results when andexanet alfa is present in the patient plasma samples. Treatment monitoring after administration of andexanet alfa should not be based on anti-FXa activity.