Arterial thromboembolism and associated antithrombin III deficiency

A patient with antithrombin III (ATT) deficiency after arterial embolism manifested an increasing requirement for heparin to adjust a partial thromboplastin time. This was corrected by dramatically increasing doses of heparin and by conversion to warfarin sodium. "Heparin-resistance" should direct the physician to examine antithrombin III levels, and ATT levels should be determined as a baseline before anticoagulation therapy.