Twenty studies (23,668 participants) were included in the review: one randomised study (136 participants), 11 prospective studies and eight retrospective studies. Newcastle-Ottawa scores ranged from 7 to 10 points.
Treatment with clopidogrel prior to cardiac surgery was associated with significant increases in mortality (OR 1.24, 95% CI 1.03 to 1.49; 15 studies; Ι²=0%), red blood cell transfusions (OR 1.82, 95% CI 1.40 to 2.37; 14 studies; Ι²=84%) and re-operations triggered by major bleeding (OR 2.15, 95% CI 1.38 to 3.34; 16 studies; Ι²=54%).
Results of the subgroup analyses indicated that discontinuation of clopidogrel less than three days prior to cardiac surgery was associated with a higher incidence of red blood cell transfusions (OR 7.56, 95% CI 2.38 to 23.99), major bleeding (OR 6.62, 95% CI 1.69 to 25.95) and re-operation (OR 3.40, 95% CI 1.51 to 7.65). Re-operation rates were significantly higher in clopidogrel-treated groups in studies published prior to 2006(OR 4.73, 95% CI 3.01 to 7.45; seven studies; Ι²=0%).
There were no differences between the clopidogrel treated groups and control groups in postoperative myocardial infarction; significant statistical heterogeneity was observed across the nine studies for this outcome (Ι²=56%).