['Utilization of the irreversible antiplatelet agent clopidogrel is increasing in the treatment acute coronary syndrome patients. Consequently, more patients are presenting for urgent cardiac surgery with an irreversible defect in platelet function. The objective of this study was to determine whether recent clopidogrel administration predicts transfusion and hemorrhagic complication in cardiac surgery patients.', 'This retrospective study included all patients undergoing isolated coronary artery bypass graft surgery (CABG), isolated valve, or CABG plus valve at a single center between 2004 and 2008. The outcomes of interest were transfusion and hemorrhagic complication. Clopidogrel stop interval was defined as the time between last dose and presentation to the operating room, and was examined in daily increments from 0 to 5 days, more than 5 days, and not receiving clopidogrel preoperatively. By logistic regression, the association of clopidogrel stop interval with transfusion and with hemorrhagic complication was examined after adjusting for other risk factors.', 'Of 3,779 patients included in this study, 26.4% (999) received clopidogrel preoperatively. The overall rates of transfusion and hemorrhagic complication were 34.1% and 4.1%, respectively. Clopidogrel use within 24 hours was an independent predictor of transfusion (odds ratio 2.4; 95% confidence interval: 1.8 to 3.3) and of hemorrhagic complication (odds ratio 2.1; 95% confidence interval: 1.3 to 3.6).'] Does clopidogrel increase blood transfusion and hemorrhagic complications in patients undergoing cardiac surgery?