Efficacy and Safety of Apixaban in the Treatment of Heparin Induced Thrombocytopenia (HIT)

Inclusion Criteria: * Hospitalized patients at MGH and participating Dana Farber/Harvard Cancer Center (DF/HCC) sites. * Patient must have a diagnosis of HIT or high clinical suspicion of HIT, with a 4 T score of ≥ 5 as calculated by the following criteria: * Thrombocytopenia * Platelet count fall \>50 percent and nadir ≥20,000/microL - 2 points * Platelet count fall 30 to 50 percent or nadir 10 to 19,000/microL - 1 points * Platelet count fall \<30 percent or nadir \<10,000/microL - 0 points * Timing of platelet count fall * Clear onset between days 5 and 10 or platelet count fall at ≤1 day if prior heparin exposure within the last 30 days - 2 points * Consistent with fall at 5 to 10 days but unclear (eg, missing platelet counts), onset after day 10, or fall ≤1 day with prior heparin exposure within 30 to 100 days - 1 point * Platelet count fall at \<4 days without recent exposure - 0 points * Thrombosis or other sequelae * Confirmed new thrombosis, skin necrosis, or acute systemic reaction after intravenous unfractionated heparin bolus - 2 points * Progressive or recurrent thrombosis, non-necrotizing (erythematous) skin lesions, or suspected thrombosis that has not been proven - 1 point * None - 0 points * Other causes for thrombocytopenia * None apparent - 2 points * Possible - 1 point * Definite - 0 points * Prior to or immediately subsequent to enrollment, the patient must have the diagnosis confirmed by Heparin-PF4 EIA or other accepted conf…