Sex-stratified association between systemic immune-inflammation index and gallstone risk: a cross-sectional study in a Chinese adult population

Introduction Gallstone disease is a prevalent biliary condition with rising incidence in China, driven by changes in lifestyle, metabolism, and inflammation. The systemic immune-inflammation index (SII), a composite marker reflecting immune and inflammatory status, has been linked to various chronic diseases. However, its association with gallstone in the general Chinese population remains unclear. This study aimed to investigate the relationship between SII and gallstone risk in a large adult cohort. Methods A cross-sectional analysis was conducted among 55,241 adults undergoing health screening. Gallstone was diagnosed via abdominal ultrasonography. SII was log-transformed (Ln-SII) to correct for skewness. Logistic regression models assessed the association between Ln-SII and gallstone risk with progressive adjustments. Smooth curve fitting and two-piece wise linear regression were used to explore potential nonlinear associations. Subgroup analyses were performed by sex. Results Gallstone was identified in2,606 participants (4.72%). After full adjustment, higher Ln SII was significantly associated with increased gallstone risk (OR = 1.10, 95% CI: 1.01–1.21, p = 0.0372). In sex-stratified analyses, a significant linear association was found in females (OR = 1.21, 95% CI: 1.06–1.39, p = 0.0059), whereas a nonlinear association emerged in males, with increased risk only above an Ln-SII threshold of 6.52. Despite these sex-specific patterns, no statistically significant interaction between sex and SII was observed. Conclusion Higher Ln SII was associated with increased gallstone risk, and sex-stratified analyses revealed distinct association patterns. However, no significant interaction between sex and SII was observed, suggesting that these differences may not represent effect modification. Further studies are needed to clarify the underlying mechanisms.