Association Between Systemic Immune-Inflammation Index and CA125 in Older Women: Insights from a Cross-Sectional NHANES Study.

Introduction: The Systemic Immune-Inflammation Index (SII) is a novel biomarker that has been implicated in the pathogenesis of various neoplastic and non-neoplastic diseases. This study aimed to evaluate the association between SII and the conventional tumor marker CA125 (Carbohydrate antigen 125) in a population of postmenopausal women. Methods: This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES), focusing on postmenopausal women with available data on SII and CA125. The SII was calculated using the formula: platelet count × neutrophil count/lymphocyte count. To evaluate the relationship between the SII and cancer antigen 125 (CA125), we conducted multivariate regression analyses. The linear association between these variables was further explored by fitting a smoothed curve to examine nuances in their relationship. Additionally, subgroup analyses were performed based on age, age at menarche and menopause, and hormone replacement therapy status to assess the heterogeneity of the relationship between SII and CA125 between different demographic groups. Results: A total of 741 postmenopausal women with a mean age of 72.0 (±8.24) years were included in this analysis. The results demonstrated a significant positive correlation between SII and CA125 levels (β = 0.01; 95% CI, 0.00-0.02, p = 0.0128). Subgroup analyses and interaction tests revealed that variables such as age, age at menarche and menopause, and hormone replacement therapy did not significantly modify this association (p > 0.05). Conclusion: This study demonstrated a positive correlation between SII and C125 in older female patients in the United States.