HIT must be distinguished from other causes of thrombocytopenia. This Anon-immune heparin associated thrombocytopenia has not been found to be associated with thrombosis and does not necessitate discontinuation of heparin. A more rapid onset of thrombocytopenia can occur in patients on heparin who have had previous exposure to heparin, usually within the preceeding few weeks. Paradoxically, patients with HIT are at higher risk of thrombosis than bleeding, even when thrombocytopenia is severe. Thrombosis may be the presenting clinical manifestation of HIT and can occur during the period of thrombocytopenia or platelet count recovery, despite discontinuation of heparin.
Most thrombotic events are venous although both venous and arterial thrombotic events can occur.
Thrombotic events typically include deep vein thrombosis, pulmonary embolism, limb arterial thrombosis, thrombotic stroke, and myocardial infarction. HIT should be considered in the differential diagnosis of patients with new or recurrent venous or arterial thromboembolism that develops during or shortly after exposure to heparin. Less frequently observed manifestations of HIT include heparin-induced skin lesions, hemorrhagic adrenal infarction, acute systemic reactions, and arterial and venous thrombotic events in unusual locations. Therapeutic decisions should not be delayed for the results of laboratory testing if the clinical suspicion of HIT is strong. Argatroban is not commercially available in Canada yet.