(A) Positive heparin-induced platelet aggregation (HIPA) or other functional assay, defined as: (B) HIT: Thrombocytopenia associated with heparin therapy, where the platelet count: (i) has decreased to <100x10(9)/L (minimum of 30% drop from the platelet count before heparin treatment), OR (ii) has decreased to <150x10(9)/L (minimum of 40% drop from the platelet count before heparin treatment, OR, (C) HITTS: Thrombocytopenia (as defined above) PLUS arterial or venous thrombosis (deep-vein thrombosis, pulmonary embolism, mesenteric venous or arterial thrombosis, acute myocardial infarction, left ventricular thrombus, ischemic stroke, or occlusion or limb arteries), diagnosed by physical exam/lab evidence and/or appropriate imaging studies (duplex ultrasound, venography, ventilation-perfusion scan, venous or arterial angiography, MRI/MRA, catheterization).