Association of neutrophil percentage-to-albumin ratio with all-cause and respiratory disease-related mortality in US adults with asthma: results from NHANES 1999-2018

Background: Systemic inflammation and immune dysregulation may be associated with asthma onset and progression. Neutrophil percentage-to-albumin ratio (NPAR) is a novel marker of systemic inflammation. We aimed to investigate the association of NPAR with all-cause and respiratory disease-related mortality in adults with asthma through NHANES 1999-2018. Methods: NPAR was calculated by neutrophil percentage (% of total white blood cell count) × 100/serum albumin (g/dl). Asthma was diagnosed by standardized questionnaire. Mortality was obtained by prospective matching with the National Death Index. Multivariate Cox proportional hazards regression analysis was used to explore these associations. Results: A total of 5042 adults with asthma were included. After a median follow-up duration of 104 months, 697 participants died, of which 101 were respiratory disease-related deaths. In fully adjusted models, NPAR was significantly and positively associated with both all-cause and respiratory disease-related mortality (hazard ratios [HR] of 1.126 and 1.194, respectively, both p < 0.05). Compared to Q1, NPAR at Q4 was associated with significantly increased all-cause and respiratory disease-related mortality (all-cause: HR 2.112, p < 0.0001; respiratory disease-related: HR 2.595, p = 0.013). NPAR was nonlinearly associated with all-cause mortality, with an inflection point of 13.76. This association was significant only after the inflection point. The effect of NPAR on all-cause mortality was more pronounced in those <60 years of age. Conclusions: Higher NPAR was associated with increased all-cause and respiratory disease mortality in US adults with asthma. Further exploration of the prognostic potential and underlying mechanisms of NPAR is needed. Clinical trial number Not applicable.