Obesity is increasingly prevalent among adolescents and is implicated in renal injury yet its cross-sectional association with renal injury remains paradoxical. Systemic inflammatory biomarkers—including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SIRI)—may be involved in this paradoxical association. Their potential role as mediators of obesity-related renal dysfunction requires longitudinal investigation. We conducted a cross-sectional analysis of 5,869 adolescents aged 12–20 years from the National Health and Nutrition Examination Survey (NHANES) 2009–2018 cycles. Renal injury was defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m² or urinary albumin-to-creatinine ratio (UACR) ≥ 30 mg/g. Obesity was defined as BMI ≥ 95th percentile for age and sex. Using survey-weighted logistic regression and causal mediation analysis with 1,000 bootstrap replications, we assessed the associations of obesity and inflammatory biomarkers with renal injury and evaluated the mediating roles of NLR, PLR, and SIRI. Among an estimated 32.98 million U.S. adolescents, 12.43% had renal injury. Obesity was inversely associated with renal injury (fully adjusted OR = 0.356; 95% CI: 0.231–0.548). NLR (OR = 1.190; 95% CI: 1.100–1.290) and SIRI (OR = 1.180; 95% CI: 1.060–1.310) were independently and positively associated with renal injury, whereas PLR showed no significant association. Mediation analysis revealed that NLR and SIRI showed statistical mediation of the obesity–renal injury association, accounting for 14.82% and 17.53% of the total effect, though effect sizes were modest, respectively (p < 0.001); PLR exhibited no mediating effect (p = 0.460). Associations were consistent across subgroups by sex, age, race, poverty status, vitamin D level, and sedentary behavior. The inverse obesity–renal injury association likely reflects hyperfiltration masking rather than true protection. Only NLR and SIRI showed significant associations with renal function indicators; PLR showed no significant association. These markers may aid risk stratification among adolescents with identified renal abnormalities, though they are not recommended as standalone screening tools. Not applicable.
Li et al. (Sat,) studied this question.