Incidence and clinical relevance of heparin‐induced antibodies in patients with deep vein thrombosis treated with unfractionated or low‐molecular‐weight heparin

Summary. The frequency of heparin‐induced thrombocytopenia (HIT) varies between different clinical treatment settings and remains unknown for patients treated with unfractionated (UFH) or low‐molecular‐weight heparin (LMWH) because of deep vein thrombosis. In this multicentre, open‐label study, 1137 patients with deep vein thrombosis were randomly assigned to UFH for 5–7 d, reviparin, a LMWH, for 5–7 d (short‐treated group) or reviparin for 28 d (long‐treated group). Heparin‐platelet factor 4 antibodies (HPF4‐A) were determined on d 5–7 and d 21. Heparin‐induced thrombocytopenia was defined by clinical evaluation. Two patients in the UFH group (incidence: 0·53%, 95% confidence interval (CI): 0·06–1·91) and two patients in the long‐treated LMWH group (incidence: 0·53%, 95% CI: 0·06–1·92) had HIT, while no HIT was observed in the short‐treated LMWH group. Pulmonary embolism developed in one of the HIT‐patients, who had HPF4‐A and was treated with UFH. On d 5–7 the incidence of HPF4‐A was 9·1% in the UFH group, 2·8% in the short‐treated LMWH group and 3·7% in the long‐treated LMWH group, with a significant increase to 20·7% in the UFH group and to 7·5% in the long‐treated LMWH group on d 21. Therefore the incidence of HPF4‐A and heparin‐induced thrombocytopenia was lower in patients treated with LMWH compared with UFH for the same duration of treatment.