Heparin induced thrombocytopenia.

Heparin induced thrombocytopenia (HIT) is a serious and life endangering complication of heparin therapy. It usually occurs after 5-14 days of continuous heparin therapy. It is immune mediated. Heparin, in the affected individual binds with platelet factor 4 (PF-4) and forms a highly antigenic Heparin PF-4 complex which leads to the generation of specific IgG Heparin PF4 antibodies (also called HIT antibodies). HIT antibodies may activate the platelets via Fcy receptor causing the release of highly coagulable micro particles which promote thrombosis--both venous and arterial. However, all patients with HIT antibodies do not progress to HIT with thrombosis (HITT). HIT can present as asymptomatic thrombocytopenia. It can also present with alarming features of venous and/or arterial thromboembolism, for example, pulmonary embolism from deep vein thrombosis (DVT), limb gangrene warranting amputation, cerebrovascular attack (CVA) or myocardial infarction (MI). Rare manifestation of HIT includes necrotizing skin lesion, acute anaphylactoid reaction following IV heparin bolus and acute adrenal apoplexy due to massive adrenal vein thrombosis. The diagnosis is based upon the combination of unexplained thrombocytopenia, demonstration of HIT antibodies, clinical profile and outcome of the case following withdrawal of heparin and administration of non-heparin anticoagulant like Lepirudin, Argatroban or Danaparoid. The choice of alternative anticoagulant depends upon the availability, cost, monitoring facilities and administrative guidelines.