Apparent heparin resistance in a patient with infective endocarditis secondary to elevated factor VIII levels

Heparin resistance (HR) is defined as increasing requirements of heparin to maintain a therapeutic activated partial thromboplastin time (aPTT). It is commonly associated with antithrombin deficiency, increased heparin clearance and elevations in heparin binding proteins. Elevated factor VIII levels can cause decrease the aPTT levels (anticoagulant effect) without disturbing heparin activity measured by anti-Xa assay (antithrombotic effect) leading to an apparent heparin resistant state rather than a true heparin resistance. We highlight the importance of increasing awareness of apparent HR and early distinction from true resistance to avoid major life threatening hemorrhagic complications. We hereby report an unusual case of heparin resistance due to increased factor VIII levels in an elderly male with infective endocarditis.