Sammour T, Singh PP, Su’a B, Zargar-Shoshtari K, Hill AG Peritoneal cytokine levels can predict anastomotic leak on the first post-operative day. Sammour T, Singh PP, Su’a B, Zargar-Shoshtari K, Hill AG Aim Accumulating evidence suggests that peritoneal cytokine concentrations may predict anastomotic leak after colorectal surgery, but previous studies have been under-powered. We aimed to test this hypothesis using a larger prospectively collected data set. Results A total of 206 patients with complete cytokine data were included. The overall anastomotic leak rate was 8.3%. Concentration levels of peritoneal IL-6 and IL-10 on day 1 were predictive of anastomotic leak (AUROC 0.72 and 0.74, P = 0.006 and 0.004, respectively). Plasma cytokine levels of IL-6 were higher on day 1 in patients who had anastomotic leak, but this was a poor predictor. Levels of other peritoneal and plasma cytokines were not predictive. Methods Patients undergoing colorectal surgery recruited as part of three previous randomised controlled trials were included. Data on peritoneal and plasma levels of IL-6, IL-8, IL-10 and TNFα on day 1 after surgery were re-analysed to evaluate their predictive value for clinically important anastomotic leak. Area under receiver operating characteristic curve analysis (AUROC) was performed. Conclusion Peritoneal levels of IL-6 and IL-10 on day 1 after colorectal surgery can predict clinically important anastomotic leak. The discriminative value in clinical practice requires further investigation. Drain cytokine concentrations