Heparininducerad

Heparininducerad refers to reactions that arise after exposure to the anticoagulant heparin, most notably heparin-induced thrombocytopenia (HIT). HIT is an immune-mediated adverse reaction in which antibodies form against the complex of platelet factor 4 and heparin, leading to platelet activation, a fall in platelet count, and an increased risk of thrombosis.

The underlying mechanism involves antibody formation against the PF4–heparin complex. This activates platelets and other cells, creating a prothrombotic state despite anticoagulation. HIT typically presents 5 to 14 days after starting heparin, or more rapidly if there has been recent exposure. It is more common with unfractionated heparin than with low-molecular-weight heparin.

Clinically, HIT may manifest as unexplained falling platelets, new thrombotic events (deep vein thrombosis, pulmonary embolism, arterial thrombosis), or less commonly, skin reactions at the injection site. Diagnosis relies on clinical suspicion supported by laboratory testing: an initial immunoassay for PF4–heparin antibodies (the 4Ts score can guide pre-test probability), with confirmation via functional tests such as a serotonin release assay.

Management requires immediate cessation of heparin and avoidance of all heparin products. Alternative anticoagulation with non-heparin agents—such as direct thrombin inhibitors (eg, argatroban, bivalirudin), fondaparinux, or danaparoid—should be started as soon as HIT is suspected. Warfarin is generally started only after platelet counts recover and overlapping with a non-heparin anticoagulant is completed. Recovery of platelet counts typically occurs within days to weeks, and long-term prognosis improves with prompt treatment.

See also: heparin-induced skin reactions, thrombocytopenia, non-heparin anticoagulants.