Heparin-induced thrombocytopenia: pathophysiology.

HIT is a procoagulant disorder that is associated with significant morbidity and mortality if undetected and untreated. It occurs in approximately 5% of all patients receiving heparin therapy. HIT can be separated into two different types based on the clinical presentation and the pathophysiological mechanism. Type I HIT is an early, mild form of thrombocytopenia that is thought to be non-immune-mediated. No therapy is necessary for this type of HIT. Type II HIT has a delayed onset and is immunologically mediated. It is the more severe form and is associated with the development of HITT. Once suspected or diagnosed, all heparin therapy must be withdrawn. The thrombocytopenia will generally resolve within several days to a week. Minimizing the risk to the patient for developing HIT is the best form of prevention currently available.