A multicenter observational study of the association between systemic immune inflammation index and adenomyosis

Adenomyosis involves aberrant inflammation and immune dysregulation in its pathogenesis. This multicenter study investigated the association between the systemic immune inflammation index (SII) and adenomyosis risk among 74,900 participants undergoing laparoscopic surgery. In this retrospective analysis of 9,333 patients and 65,567 controls, elevated SII levels-after adjustment for 10 confounders including intrauterine device (IUD) use, cesarean history, and hypertension-showed a consistent, stepwise association with increased adenomyosis risk, whether SII was analyzed as a categorical or continuous variable. Notably, this upward trend plateaued when SII reached or exceeded 1,500. Subgroup analyses revealed that this significant positive association persisted independently in women with a body mass index (BMI) < 24 kg/m², those with no cesarean delivery history, and non-IUD users. These findings demonstrate an association between elevated SII and increased adenomyosis risk, supporting its potential role in risk evaluation for these three specific subgroups.