Heparin-induced thrombocytopenia

Thrombocytopenia is the most common event in HIT and occurs in at least 90% of patients depending on the definition used.

The diagnosis of HIT should be based on both HIT-associated clinical events and detection of HIT antibodies in patient serum or plasma.

A patient who appears clinically to have HIT but has negative sensitive HIT antibody tests does not have HIT according to the review's clinicopathological definition.

A patient with HIT antibody seroconversion alone but no thrombocytopenia or other adverse events does not meet the review's definition of HIT.

HIT is associated with increased thrombin generation in vivo and increased risk for arterial and especially venous thrombosis.

Pathogenic HIT antibodies are directed against neoepitopes on PF4 that are expressed when PF4 is bound to heparin or certain other polyanions.

The review describes a central role for thrombin generation in HIT pathogenesis, with platelet, endothelial-cell, and monocyte activation contributing to the prothrombotic state.

HIT is a transient prothrombotic disorder initiated by heparin in which thrombocytopenia is caused by antibody-mediated platelet activation.

Alternative non-heparin anticoagulant therapy reduces the risk of subsequent thrombosis in HIT.