Systemic inflammatory markers in relation to lung function in NHANES. 2007-2010

Background: Low-grade systemic inflammation, mainly assessed by C-reactive protein (CRP), has been associated with impaired lung function. Few studies have studied if CRP, blood eosinophils, and blood neutrophils offer additive information in relation to lung function. Objectives: To analyse associations between lung function and CRP, blood eosinophils, and blood neutrophils, with special regard to additive information of combining the inflammatory markers. Methods: Cross-sectional study on 7753 participants, 20-80 years of age, in the National Health and Nutrition Examination Survey. Gender-based tertiles for CRP, blood eosinophils, and blood neutrophils were analysed in relation to the following lung function parameters: forced expiratory volume in 1 s (FEV1% predicted), forced vital capacity (FVC % predicted), and FEV1/FVC ratio. Results: CRP, blood eosinophils, and blood neutrophils levels were inversely related to FEV1 and FVC. Only blood eosinophils and blood neutrophils were inversely related to FEV1/FVC ratio. Further, lower lung function was found with increased number of elevated inflammatory markers in the highest tertile (one, two or three vs. non elevated) for FEV1 (beta-coeff., -2.20, -4.43, and -6.43, p < 0.001) and FVC (beta-coeff., -1.70, -3.15 and -5.33, p < 0.001), respectively. Conclusions & clinical relevance: CRP, blood eosinophils, and blood neutrophils offer independent and additive information in relation to lower FEV1 and FVC in the general population. This indicates that a combination of biomarkers yields more information than the biomarkers assessed individually.