Nonlinear association between neutrophil-to-lymphocyte ratio and asthma in children and adolescents in the United States: a cross-sectional study.

Background: The neutrophil-to-lymphocyte ratio (NLR) is a marker of systemic inflammation associated with various diseases including respiratory conditions. However, the relationship between NLR and asthma in the pediatric population remains underexplored.

Purpose: This study aimed to explore the association between NLR and asthma in children and adolescents and assess its potential role as a predictive biomarker for pediatric asthma.

Methods: We retrospectively analyzed the medical records of 12,974 children and adolescents from the National Health and Nutrition Examination Survey in 2011-2020. NLR was defined as the ratio of NLR counts. Asthma was diagnosed using a structured questionnaire. Multivariate logistic regression models were used to evaluate the association between NLR and asthma. A restricted cubic spline was used to explore nonlinear relationships, and a threshold analysis was conducted to identify potential cutoff values for the NLR.

Results: A total of 12,974 children and adolescents were included (male: 6,686 [51.5%]; mean [interquartile range] age, 10 [5.0-14.0 years]). After the adjustment for confounders, participants with the highest versus lowest NLR exhibited a significantly elevated risk of asthma (odds ratio [OR], 1.39; 95% confidence interval [CI], 1.13-1.71). Additionally, a multivariate restricted cubic spline analysis revealed a nonlinear relationship between NLR and asthma (P=0.023). A threshold analysis revealed that an NLR<2.23 was significantly associated with an increased risk of asthma (OR, 1.23; 95% CI, 1.05-1.45), while an NLR≥2.23 showed no significant association. A subgroup analysis revealed no interactive role of NLR and asthma.

Conclusion: Our findings indicate a nonlinear saturation-effect relationship between NLR and asthma in children and adolescents.