Increased Systemic Immune-Inflammation Index as a Novel Indicator of Alzheimer's Disease Severity

Introduction: Inflammatory processes and neurodegeneration are common features of Alzheimer's disease (AD). The systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) are easily accessible, cost-effective prognostic indicators of inflammation status. We assessed the diagnostic value of SII and compared the efficacies of NLR, PLR, and SII in predicting AD severity. Materials and Methods: Between January 2021 and December 2022, this prospective, cross-sectional clinical study included 175 patients with AD and 61 controls. SII, NLR, and PLR were calculated. Results Age, white blood cell and lymphocyte counts, and NLR and PLR values were significantly different between the patient and control groups (P <.05). Age, hemoglobin, neutrophil, NLR, and SII values were significantly different among dementia severity subgroups (P <.05). Compared with PLR and SII, NLR was more strongly correlated with dementia severity. In the analysis of adjusted data by gender, it was found that hemoglobin level is significantly negatively associated with dementia severity in males, while in females, age and PLR are significantly positively associated with dementia severity, and lymphocyte count and SII are negatively associated. Conclusion: SII, a novel inflammatory marker, was associated with dementia severity in patients with AD. Compared with PLR and SII, NLR was more strongly correlated with dementia severity. In future studies with larger populations, SII and NLR values can be used to determine dementia severity and establish follow-up plans for patients with high dementia risk.