Nonlinear association between neutrophil percentage to high-density lipoprotein ratio and asthma in older population: a cross-sectional study

Abstract Background Asthma, a chronic allergic condition, is commonly associated with elevated eosinophil levels. However, the relationship between the neutrophil percentage and the high-density lipoprotein ratio (NHR) in asthma remains poorly defined. This study aims to clarify the association between NHR and asthma in the elderly population in the US. Methods Leveraging data from the national health and nutrition examination survey (NHANES) from 2015 to 2018, this study investigated the association between NHR and asthma among individuals aged 60–80 years in the US. Logistic regression models, adjusted for multiple covariates, were employed to evaluate these associations. In addition, smooth curve fitting was applied to identify potential nonlinear relationships and threshold effects. Subgroup analyses were further conducted to assess variations across different population groups. Results The study included 1,514 participants, with a median age of 70.0 years and an asthma prevalence of 14.53%. After adjustment for relevant covariates in Model III, a statistically significant negative association between NHR and asthma was observed (OR = 0.130, 95% CI: 0.040–0.360, p < 0.001). This relationship was nonlinear, with an inflection point at NHR = 1.637. Beyond this threshold, the negative association remained significant (OR = 0.160, 95% CI: 0.040–0.680, p = 0.013). Receiver operating characteristic (ROC) curve analysis demonstrated a predictive value of NHR for asthma, with an area under the curve (AUC) of 0.615 when NHR was ≥ 1.430. Conclusion This study reveals a significant association between NHR and asthma among individuals aged over 60 in the US, indicating that as NHR increases beyond 1.637, the likelihood of asthma decreases.