Platelet counts of patients after cardiopulmonary bypass. Patients were grouped depending on the presence of anti–protamine-heparin antibodies (absent, group A [n = 534]) and the capability of these antibodies to activate platelets in vitro (non–platelet-activating anti–protamine-heparin antibodies, group B [n = 50]; platelet-activating anti–protamine-heparin antibodies, group C [n = 7]). The means of platelet counts at the corresponding day after surgery are plotted. The insert table shows the P values comparing the different platelet count curves with each other.