Lymphocyte count and systemic immune-inflammation index (SII) as novel biomarkers for cognitive impairment: A cross-sectional study analysis

Early detection of cognitive dysfunction through reliable biomarkers remains a critical challenge in geriatric medicine. While conventional peripheral blood parameters offer convenient and cost-effective biomarker potential, previous studies have been limited by their focus on isolated cell populations. This study investigates both individual blood cell parameters and their derived ratios to comprehensively evaluate their relationship with cognitive function. In this cross-sectional conducted from 2022 to 2024, we enrolled 109 participants (51 with cognitive impairment and 58 controls) from the Haikou City Community Health Service Center. Cognitive function was assessed using the Montreal Cognitive Assessment (MoCA). We analyzed 26 blood parameters, including traditional metrics and calculated indices such as lymphocyte-to-monocyte ratio, platelet-to-lymphocyte ratio, and systemic immune-inflammation index (SII). The relationship between these parameters and cognitive domains was evaluated using comprehensive statistical analyses. Fifteen parameters showed significant differences between groups. Binary logistic regression identified SII as a risk factor (OR: 1.008, 95% CI: 1.003-1.012, P = .002). The receiver operating characteristic curve analysis indicated that the diagnostic accuracy of SII (AUC = 0.911, 95% CI: 0.856-0.966) was significantly superior to that of the sole parameter, the number of lymphocyte count (AUC = 0.702, 95% CI: 0.604-0.801). Our findings suggest that lower lymphocyte counts and elevated SII levels are associated with increased risk of cognitive impairment. These results provide new insights into the relationship between systemic inflammation and cognitive decline, with potential implications for clinical practice.