We describe the case of a 38-year-old man with a history of chronic portal vein thrombosis who presented with abdominal pain after a transjugular intrahepatic portosystemic shunt procedure. Under anticoagulation therapy with rivaroxaban, he experienced active splenic bleeding, leading to hemodynamic instability. Emergency interventions, including andexanet alfa and nanoparticle administration, successfully stopped the bleeding. However, routine tests showed persistently high rivaroxaban levels despite reversal with andexanet alfa. This case report shows that next to standard anti-Xa activity assay, high-performance liquid chromatography is as well unreliable in this regard. In contrast, viscoelastic tests might better serve as indicators of the efficacy of the reversal. The availability of modified anti-Xa tests is urgently needed, to monitor the effects of andexanet alfa reversal.