First occurrence of ahir-ab of the IgG class measured by an ELISA as described under “Patients, materials, and methods.”

Eighty-four patients had ahir-ab develop during the first course of treatment with r-hirudin. Sixty-one of these were evaluable for determination of ahir-ab on the first day of lepirudin treatment (n = 54) or on the day of cessation of lepirudin (n = 7). The 20 patients who became ahir-ab positive during the follow-up period are not included in this Figure.