Diagnostic Performance of CBC-Derived Inflammatory Ratios (SII, NLR, PLR) for Identifying Biopsy-Proven Microscopic Gut Inflammation Despite Normal Endoscopy

Background Intestinal inflammation may be present in the early stages without endoscopic abnormalities, making timely diagnosis difficult. The inflammatory ratios calculated from complete blood count (CBC) have been proposed as noninvasive markers of inflammatory activity; among these, three are noteworthy: the neutrophil-to-lymphocyte ratio (NLR), the platelet-to-lymphocyte ratio (PLR), and the systemic immune-inflammation index (SII). Methods A cross-sectional analytical study was conducted among 350 adults undergoing upper gastrointestinal endoscopy or colonoscopy with biopsy. Patients were divided into two groups: Group A (patients with normal endoscopy and normal biopsy; n=106) and Group B (patients with normal endoscopy and biopsy-proven microscopic inflammation; n=244). Hematological parameters were obtained before the procedure and used to calculate CBC-derived inflammatory ratios. To compare inflammatory indices between groups, Mann-Whitney U tests were used. Binary logistic regression was used to evaluate associations between inflammatory indices and biopsy-proven microscopic gut inflammation after adjustment for selected clinical variables. Receiver operating characteristic (ROC) curve analysis was performed to assess the discriminatory performance of NLR, PLR, and SII. Results NLR, PLR, and SII were significantly elevated in those with biopsy-proven microscopic inflammation in the absence of endoscopic inflammation (all p<0.001). Multivariable logistic regression demonstrated significant associations between NLR (odds ratio (OR)=1.57, 95% confidence interval (CI): 1.340-1.835, p<0.001), PLR (OR=1.012, 95% CI: 1.004-1.020, p=0.003), and SII (OR=1.025, 95% CI: 1.019-1.031, p<0.001) and biopsy-proven microscopic gut inflammation. ROC analysis showed that SII had the highest discriminatory performance (area under the curve (AUC)=0.776, 95% CI: 0.720-0.831), followed by PLR (AUC=0.729, 95% CI: 0.668-0.790) and NLR (AUC=0.684, 95% CI: 0.620-0.748). Conclusion CBC-derived inflammatory ratios, especially SII, could serve as simple, inexpensive, and non-invasive adjunctive markers for identifying biopsy-proven microscopic gut inflammation despite normal endoscopic findings. Their use may provide additional information for identifying patients who may warrant further gastrointestinal evaluation.