Association between immune-inflammatory biomarkers (NLR, PLR, SII, SIRI) and obesity in adults: a systematic review and meta-analysis

Obesity is regarded as a chronic, low-grade systemic inflammatory condition. However, whether immune–inflammatory indices derived from routine peripheral blood tests—including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI)—can accurately reflect obesity-associated inflammation remains controversial, as existing studies have reported inconsistent findings. Comparing these indices between people with obesity and people without obesity, and further evaluating sources of heterogeneity and their potential clinical implications, is of considerable significance for clarifying their role in obesity research and clinical application.

Relevant studies published up to September 30, 2025, were systematically searched in PubMed, EMBASE, the Cochrane Library, and Web of Science databases. A meta-analysis was conducted using standardized mean differences (SMDs) to evaluate overall effects, with additional subgroup and sensitivity analyses performed (PROSPERO registration number: CRD420251247523).

A total of 30 studies were included, comprising 94,408 people with obesity and 129,927 people without obesity as controls. The meta-analysis demonstrated that NLR (SMD = 0.46, 95% CI: 0.10–0.82, p < 0.001), SII (SMD = 2.45, 95% CI: 0.89– 4.01, p < 0.001), and SIRI (SMD = 0.84, 95% CI: 0.47–1.22, p < 0.001) were significantly higher in the group of people with obesity compared with controls, whereas PLR showed no statistically significant difference (SMD = 0.00, 95% CI: −0.08–0.09, p > 0.05). Subgroup analyses indicated that these associations were more prominent in studies defining obesity by BMI, among individuals with chronic comorbidities, and within Asian and American populations.

NLR, SII, and SIRI may serve as potential low-cost biomarkers reflecting systemic inflammation associated with obesity, while PLR appears to have limited applicability. Future high-quality prospective studies are needed to validate their clinical utility in obesity risk stratification, prediction of complications, and monitoring of therapeutic responses, as well as to explore the potential value of combining these indices with traditional inflammatory and metabolic biomarkers.