[Heparin-induced thrombocytopenia and thrombosis. Thrombosis as an early cardinal symptom of heparin allergy].

Apart from bleeding complications, heparin-induced thrombocytopenia (HIT) type II is the most severe side effect of heparin therapy. It is widely agreed that its most important clinical symptom is thrombocytopenia, with or without thromboembolism.Assuming, unlike other authors, that thrombosis is the leading clinical symptom of HIT type II, we investigated the frequency of an immunological reaction indicative of HIT type II in patients suffering from thrombosis. From January 1999 to December 2000, 77% ( n=6713) of our in-patients received heparin for more than 5 days as thrombosis prophylaxis. When thrombosis was suspected on the grounds of clinical appearances, the patient concerned underwent phlebography, and two different serological tests for anti-heparin antibodies were also carried out. In such cases, patients were immediately switched to hirudin instead of heparin. In 29 out of 101 patients, the clinical suspicion of thrombosis was confirmed. Three patients developed pulmonary embolism. In 4 patients both serological tests revealed the presence of anti-heparin antibodies. Three of the remaining 72 patients with negative phlebography results were found to have antibodies on serological testing. In none of the 7 patients with a confirmed diagnosis of HIT type II was the classical sign of thrombocytopenia was present. Even with thorough clinical and phlebographic examinations, the incidence of HIT type II is only 0.13% in our institution. One of the 7 patients with thrombosis was not thrombocytopenic but did show the typical immunological reaction. Since the incidence of HIT type II is low and thrombocytopenia is not a reliable indicator for HIT II, the need for frequent thrombocyte counts (twice weekly) should be reconsidered.However,patients developing thrombosis while receiving heparin need to be treated for clinically suspected HIT type II until the final diagnosis is made.