Table 1. Clinical Features Consistent/Not Consistent with HIT.

Consider HIT

HIT Unlikely

Following clinical symptoms within 4-14 days of new heparin therapy or within 24 hours of heparin re- exposure* ➢absolute thrombocytopenia (<150K/μL) ➢relative thrombocytopenia (30-50% drop from baseline platelet count) ➢new or progressive arterial or venous thrombosis on heparin therapy ➢new thrombocytopenia and/or thrombosis presenting 14-30 days after recent hospitalization and heparin exposure ➢thrombosis at catheter sites ➢thrombosis at unusual sites (venous limb gangrene, skin necrosis, spinal ischemia, cerebral venous thrombosis) ➢bilateral adrenal hemorrhage (secondary to adrenal thrombosis) ➢skin necrosis at subcutaneous injection sites ➢severe thrombocytopenia (< 20K/μL) in association with DIC or extensive thrombosis

➢pancytopenia or chronic thrombocytopenia ➢petechiae or hemorrhage in the absence of DIC ➢ thrombocytopenia: within 24-72 hours in patients without prior heparin exposure in association with intra-aortic balloon pump, ventricular assist device or extracorporeal membrane oxygenation in patients with documented severe bacterial, fungal or viral infection after recent chemotherapy or pelvic radiation with microangiopathic changes on blood film in absence of DIC within 72-96 hours of cardiopulmonary bypass within 24-96 hours after cardiogenic shock from splenic sequestration

^*Re-exposure within three months of prior heparin therapy

Abbreviations: DIC, disseminated intravascular thrombosis