Ten studies (32,629 patients, range 130 to 28,871) were included in the systematic review. Three studies (670 patients) were randomised controlled trials (RCTs): two were rated excellent and one was rated poor in the quality assessment. The seven non-randomised trials (31,953 patients) were rated poor in the quality assessment.
RCTs: The difference between statins and controls for incidence of CIN was not statistically significant (OR 0.76, 95% CI 0.41 to 1.41). There was no evidence of heterogeneity (I2=0%).
Non-RCTs: The pooled effect size was statistically significant (OR 0.60, 95% CI 0.36 to 1.00). There was strong evidence of heterogeneity (I2=88%). Sensitivity analyses that removed influential studies resulted in a loss of statistical significance.
Subgroup analyses: There was a trend towards statistical significance for acute statin use prior to a planned percutaneous coronary intervention (OR 0.73, 95% CI 0.53 to 1.01; four studies). CIN reduction was not statistically significant for chronic statin use. No statistically significant effects were found in any of the other subgroups examined.