Clinical value of the systemic immune-inflammation index in patients with Crohn disease

The systemic immune-inflammation index (SII), platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR) are emerging biomarkers that reflect the immunological and inflammatory states of an organism. The calculation formula for SII is neutrophil (N) * platelet (P)/lymphocyte (L). However, the clinical relevance of SII in Crohn disease (CD) has not yet been explored. The primary aim of this study was to investigate the associations between SII, PLR, and NLR and CD, and to compare their respective potentials in evaluating disease activity. Our retrospective study included 119 CD patients and 121 sex- and age-matched healthy individuals who visited our hospital between February 2014 and February 2023. Clinical data and laboratory indices for all participants were retrieved from the hospital's medical record system. Disease activity in CD patients was assessed and quantified using the CD activity index. The SII was significantly higher in CD patients in comparison with healthy individuals (all P <.05). Among CD patients, males exhibited higher SII values than females, and patients with a low body mass index had higher SII values than those with a high body mass index (P <.05). SII, PLR, and NLR demonstrated numerically stronger positive correlations with CD Endoscopic Index of Severity (R = 0.298-0.370, P <.01) and Simple Endoscopic Score for CD (R = 0.309-0.382, P <.01) compared to CRP (R = 0.252, P = .009; R = 0.295, P = .002). Furthermore, multiple linear regression analysis revealed an independent association between penetrating disease and SII (beta = 0.455, t = 5.250, P <.001). The SII exhibited superior diagnostic performance for penetrating CD compared to PLR, NLR and CRP, demonstrating an area under the receiver operating characteristic (ROC) curve of 0.710. The cutoff value of SII was determined to be 1745.85, with a sensitivity of 0.615 and specificity of 0.783. We demonstrated that SII levels were significantly higher in CD patients compared to healthy individuals and were positively correlated with disease activity in CD. Furthermore, SII showed superior diagnostic performance in ruling out non CD compared to PLR, NLR and CRP.