Dear Sir,

Heparin-induced thrombocytopenia (HIT) associated with severe thrombotic events is a well-recognized complication of heparin therapy. The frequency of HIT var-ies widely in different reports and cumula-tive data suggest a prevalence of about 1–5% in patients treated with unfractionated hepa-rin [1, 2]. In most cases HIT manifests with platelet counts below 100! 103/ml within 5–10 days after heparin therapy. An immu-nological mechanism has been emphasized to be involved in the development of HIT and thrombosis [3, 4]. It has been proposed that heparin complexed to platelet factor 4 (PF4) is a target for IgG antibodies. Th