ObjectiveEarly identification of complicated acute diverticulitis(cAD) is especially significant for clinical physician and surgeon to reduce the antibiotic usage and the risk of emergency surgery. This study was aimed to investigate the significance of immature granulocyte(IG) count in early prediction for right-side(Rt-side) cAD.MethodsThe patients with Rt-side colonic acute diverticulitis was enrolled between January, 2019 and March, 2024, and divided into complicated and simple acute diverticulitis group(cAD and sAD). The data about demographic, clinical and laboratory parameters were collected and compared. Logistic regression analysis and receiver operator characteristic(ROC) curves were used to assess the predictive values of these parameters for Rt-side complicated diverticulitis.Results289 participants who met the inclusion criteria were followed as 31 patients in cAD group and 258 in sAD group. Compared to sAD group, cAD group had the higher body mass index(BMI) and peripheral blood routine parameters, especially IG count, systemic immune inflammation index(SII) and neutrophil-to-lymphocyte ratio(NLR), with the statistically significant differences(P<0.001). Moreover, logistic regression analysis indicated that IG count was a significant and independent predictors for cAD(OR 4.92, 95%CI 3.86–8.39). In the ROC analysis, area under the ROC curves (AUC) was found for IG count(0.93(95%CI 0.88–0.99) ) and SII(0.88(95%CI 0.820–0.95)). The optimal cut-off value of IG count was 0.10 with the largest sensitivity of 80.60% and specificity of 100.00% for identifying Rt-side colonic complicated diverticulitis.ConclusionIG count was a more comparable and independent predictor for Rt-side colonic complicated diverticulitis with a largest AUC than other markers in complete blood count (CBC). Given its early arise, easy accessibility and no-radiation, it can largely convince physicians’ decision-making of antibiotic abuse and surgeons’ early intervention in Rt-side colonic cAD.