Prevalence of anti-protamine and anti–protamine-heparin antibodies in patients undergoing cardiac surgery at different time points. Binding of IgG to either protamine (left) or protamine-heparin complexes (right panel) was assessed by EIA in patients undergoing cardiopulmonary bypass (n = 591) before surgery (day 0) and at day 6 and day 10 after surgery. In a subgroup of 161 patients, a follow-up sample was available more than 120 days after surgery.