Association between neutrophil percentage to albumin ratio and chronic obstructive pulmonary disease in adult population: a cross-sectional study and verification

Abstract Background Chronic obstructive pulmonary disease (COPD), a prevalent chronic respiratory disorder, has prompted growing interest in the neutrophil percentage to albumin ratio (NPAR) as a novel inflammatory biomarker. However, the precise relationship between COPD and NPAR dynamics remains elusive. Methods This study investigated the correlation between NPAR and COPD in adults using National Health and Nutrition Examination Survey (NHANES) data from 2015 to 2018. Logistic regression models and smoothed curve fitting showed a threshold effect and two-segment linear regression. Subgroup analyses were conducted to assess demographic differences, strengthening the study’s reliability. The research included 729 COPD patients and 530 controls, identifying factors affecting NPAR in COPD patients and confirming the NPAR-COPD link with Pearson correlation. Results This study found that COPD patients had significantly higher NPAR than healthy controls (HCs) ( p < 0.05), with older patients (≥ 60 years) showing higher NPAR than younger ones ( p = 0.051). After adjusting for covariates, a significant link between COPD and NPAR was observed (OR = 1.016, 95% CI: 1.003–1.029, p = 0.017). The risk association was nonlinear, with an inflection point at NPAR of 9.36. Linear regression analysis suggested that factors like hypertension, hemoglobin, WBC count, neutrophil count, lymphocyte percentage, ALT, and AST could influence the NPAR index in COPD patients (all p < 0.05). The ROC curve analysis showed an AUC of 0.648, which improved to 0.778 upon validation with a retrospective cohort model. Conclusion This study reveals a significant correlation between elevated NPAR and COPD, particularly in the presence of aged above 60 years.