Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy caused by an antibody against heparin/Platelet Factor 4 (PF4) complex. It complicates the treatment with unfractionated heparin (UFH). The aim of the study was to assess the interest of using confirmatory test in ELISA with use of high concentration of heparin (100 UI/mL) in patients (n=15) with discordance between platelet activation test and ELISA test. We obtained a rate inhibition higher than 50% in 86% of patients was observed. We conclude that inclusion of the high heparin confirmatory procedure in ELISA demonstrate the dependent heparin character of the antibodies but does not improve diagnostic specificity. In addiction a 2-fold increase in final test cost is observed.