Aim: Perforation is the most common complication of acute appendicitis (AA) and is also a significant cause of infertility among women. One significant challenge for accurate and timely diagnosis of AA before perforation occurs is the limited availability of sensitive and specific blood biomarkers. Although previous studies have proposed hyperbilirubinemia as a biomarker for predicting impending perforation, additional biomarkers with improved specificity and sensitivity are greatly needed. Recently, eosinopenia and altered neutrophil/leukocyte ratio have been proposed as candidate biomarkers for monitoring several emergency situations, such as sepsis. In this study, we aimed to determine whether several peripheral blood parameters, including bilirubin level, total numbers of eosinophils, platelets, and neutrophils, neutrophil/leukocyte ratio, and mean platelet volume, are predictive for impending perforation in patients with AA.Materials and Methods: All cases with histopathologically confirmed AA who were admitted to our hospital between January 1, 2012 and December 31, 2013 were included in this retrospective study. The bilirubin levels, total numbers of eosinophils, platelets, and neutrophils, neutrophil/leukocyte ratios, and mean platelet volume levels were compared for non-perforated and perforated AA patients. To compare the groups, the post hoc Mann-Whitney-U test was used to analyze non-parametric continuous variables; also, the receiver operating characteristics (ROC) test was used for accuracy.Results: Among the 590 patients who received a pathological diagnosis of AA, 10.8% progressed to perforation of the appendix. Significant differences in total leukocyte, neutrophil, and eosinophil counts, neutrophil/leukocyte ratios, and bilirubin levels were found between the non-perforated and perforated AA cohorts. The areas under the curve (AUCs) for each parameter were 0.64, 0.63, 0.66, 0.62, and 0.60, respectively. Neutrophil/leukocyte ratios >=72.2% had the highest sensitivity (84.4%) and eosinophil counts of <=20/mcl had the highest specificity (76.8%) in predicting perforation.Conclusion: While eosinopenia alone does not appear to be a marker for perforation, eosinopenia accompanied by higher neutrophil and leukocyte counts, a higher neutrophil/leukocyte ratio, and a higher bilirubin level can be used as a biomarker panel for predicting perforation in cases of AA.