Transient increase of IgG binding to PF4/H in CPB patients after surgery. A total of 166 patients undergoing CPB surgery were recruited into the study. Anti-PF4/H IgG binding was determined preoperatively, 10 days later, and reanalyzed around 4 months postoperatively. The differences between the OD values on day 10 or > 4 months and baseline OD values are shown. The means are shown by solid lines. (A) Patients were classified into responders or nonresponders according to the increase in anti-PF4/H IgG serum binding from day 0 to day 10, with a threshold of ΔOD = 0.5 (hatched line). (B) At approximately 4 months after CPB, anti-PF4/H Abs had decreased and responders became indistinguishable from nonresponders. Very few patients remained above the threshold for responders (hatched line).