IntroductionAnastomotic leak (AL) is a serious complication in colorectal surgery due to its increase in morbidity and mortality. The aim of this prospective non-randomised study is to determine whether C-reactive Protein (CRP) is useful as a predictor of AL in patients undergoing open versus laparoscopic surgery. MethodsA total of 168 patients undergoing elective colorectal surgery were included. CRP was measured daily during the first 5 postoperative days. Complications, specially AL, were analyzed. ResultsFollowing an open approach 32 patients (45.7%) presented complications, 15 (18.7%) in the laparoscopic group and 12 (29.4%) in the converted group (P=0.153). Following open surgery 9 patients experienced AL, 5 were detected in the laparoscopic group and none in those converted (P=0.153). There were significant differences in CRP values between the 3 groups (P=0.03). ROC Curves showed AUC for the open and laparoscopic approach of 0.731 and 0.760 respectively. On day 4 the AUC was 0.867 for the open group and 0.914 for the laparoscopic group.Cut-off points on day 4 were: Open: 159.2mg/L; sensitivity 75%, specificity 89% and NPP 96% (P<0.001). Following laparoscopic surgery the cut-off point was 67.3%; sensitivity 100%, specificity 89.5% and NPP 100% (P=0.016). ConclusionCRP on day 4 is useful to diagnose AL. Different cut-off values should be taken into account depending on the approach used.