**6. Summary**

HIT represents a rare but potentially life threatening complication of heparin therapy. Its pathogenesis is based on an immunological reaction specifically the formation of antibodies directed against a complex of heparin and PF-4. Secondary exposure to heparin triggers a reaction leading to activation of platelets, their aggregation and adhesion to endothelium leading to formation of clots (80% in the venous system and 20% in arteries) and subsequent thrombotic events.

The definitive diagnosis of HIT requires sophisticated laboratory tests that may take a while to get results from. Therefore treatment should be initiated before final results are obtained based on high clinical suspicion. The most important principles of therapy include: discontinuation of any form of heparin therapy, treatment with indirect inhibitors of factor Xa or direct thrombin inhibitors and reversal of vitamin K antagonists if they were used previously. Additionally, transfusion of platelets should be avoided since it will only precipitate their activation and aggravate the clinical symptoms.
