Kaplan-Meier analysis of the proportion of patients with heparin-dependent antibodies after an episode of heparin-induced thrombocytopenia. The time (in days) to a negative test by the activation assay (144 patients) or the antigen assay (93 of the 144 patients) is shown. All 144 patients initially had positive tests for heparin-dependent antibodies and underwent subsequent testing within 180 days. The date the test result became negative was estimated to be the date midway between the date of the last positive test and the date of the first negative test. The antigen assay tended to become negative more slowly than did the activation assay (P = .007 by the sign test). The bars indicate 95% confidence intervals. Reprinted from Warkentin and Kelton⁶⁴  with permission.