The influence of individual characteristics and non-respiratory diseases on blood eosinophil count.

BACKGROUND: Blood eosinophil (B-Eos) count is an emerging biomarker in the management of respiratory disease but determinants of B-Eos count besides respiratory disease are poorly described. Therefore, we aimed to evaluate the influence of non-respiratory diseases on B-Eos count, in comparison to the effect on two other biomarkers: fraction of exhaled nitric oxide (FeNO) and C-reactive protein (CRP), and to identify individual characteristics associated with B-Eos count in healthy controls. METHODS: Children/adolescents (<18 years) and adults with complete B-Eos data from the US National Health and Nutritional Examination Surveys 2005-2016 were included, and they were divided into having respiratory diseases (n = 3333 and n = 7,894, respectively) or not having respiratory disease (n = 8944 and n = 15,010, respectively). After excluding any respiratory disease, the association between B-Eos count, FeNO or CRP, and non-respiratory diseases was analyzed in multivariate models and multicollinearity was tested. After excluding also non-respiratory diseases independently associated with B-Eos count (giving healthy controls; 8944 children/adolescents and 5667 adults), the independent association between individual characteristics and B-Eos count was analyzed. RESULTS: In adults, metabolic syndrome, heart disease or stroke was independently associated with higher B-Eos count (12%, 13%, and 15%, respectively), whereas no associations were found with FeNO or CRP. In healthy controls, male sex or being obese was associated with higher B-Eos counts, both in children/adolescents (15% and 3% higher, respectively) and adults (14% and 19% higher, respectively) (p < 0.01 all). A significant influence of race/ethnicity was also noted, and current smokers had 17% higher B-Eos count than never smokers (p < 0.001). CONCLUSIONS: Non-respiratory diseases influence B-Eos count but not FeNO or CRP. Male sex, obesity, certain races/ethnicities, and current smoking are individual characteristics or exposures that are associated with higher B-Eos counts. All these factors should be considered when using B-Eos count in the management of respiratory disease.