Patterns of thrombocytopenia for HIT and conditions confused for HIT. (A) Time course for drop in platelets (blue) in response to increase in HIT antibody titer (orange squares). Recovery of platelet count with discontinuation of heparin and transition to direct thrombin inhibitor. (B) Rapid onset HIT. Patient was previously treated with heparin and developed rapid onset of thrombocytopenia with heparin exposure. (C) Thrombocytopenia with extracorporeal membrane oxygenation (ECMO)—not HIT. Rapid and sustained thrombocytopenia is seen with initiation of ECMO due to platelet consumption within the circuit. (D) Thrombocytopenia after cardiopulmonary bypass (CPB)—not HIT. Platelet drop within 1-3 days after CPB, followed by recovery.