Comparison of antibody isotype profiles between previous episode of HIT and antibodies generated after heparin reexposure. For each of 5 patients (3, 8, 15, 16, 20), the isotype profiles were identical for the previous HIT episode and the antibodies generated after UFH rechallenge, whereas for the 2 remaining patients (10, 11), 1 of the antibody isotypes present with the previous HIT episode was not regenerated upon UFH rechallenge. The size and color of the circles indicate the strength of EIA reactivity and the antibody isotype, respectively. *Indicates that reactivity in the EIA was not inhibited by >30% in the presence of high heparin.