[The HITT syndrome: heparin-induced thrombocytopenia and thrombosis as a cause of paradoxically occurring thromboembolisms].

Heparin since the early sixties has played an important part in prevention and treatment of thromboembolic processes. It has hardly any side effects like allergic reactions but haemorrhage is seen more frequently. A less well-known complication is so-called heparin-induced thrombocytopenia and thrombosis (HITT). There are two different forms: a mild thrombocytopenia, characterised by a decrease in platelet count to 100-150 x 10(9)/l. This form causes no clinical symptoms. The more severe form occurs between the 7th and the 11th day after heparin administration and is characterised by paradoxically occurring thromboembolic complications. This syndrome results from formation of an antigen-antibody complex. If heparin has been administered in the past patients may develop this severe form at the moment of renewed administration. In our hospital during the past 8 years we observed 9 patients with the HITT syndrome presenting with thromboembolic complications. A thrombocyte aggregation test is diagnostically useful. Heparin-free plasma of the patient is mixed with donor thrombocytes, and heparin is added; in the HITT syndrome aggregation occurs. The main therapy is stopping the heparin administration and giving antiaggregants such as dextrans.