Prevalence and potential risk factors for T2-low asthma among school-aged children in the National Health and Nutrition Examination Survey, 2007-2012.

Background: T-helper 2 (T2)-high asthma has been assumed to be the most common asthma endotype in school-aged youth.

Objective: To assess the prevalence and potential risk factors for T2-low asthma in a representative sample of U.S. children.

Methods: Cross-sectional study of 4,284 children aged 6 to 17 years in the 2007-2012 National Health and Nutrition Examination Survey. Using available biomarkers, T2-low asthma was defined by an absolute peripheral blood eosinophil count (AEC) <300 cells/uL and fractional exhaled nitric oxide (FeNO) <25 ppb, and T2-high asthma was defined by AEC ≥300 cells/uL or FeNO ≥25 ppb. In a secondary analysis, an AEC <428 cells/μL and a FeNO <32.5 ppb was used to define T2-low asthma. Multinomial logistic or linear regression was used for the multivariable analysis.

Results: Among 505 children with asthma, 231 (45.7%) had T2-low asthma. Compared with controls, those with T2-low asthma were 1.1 to 2.1-times significantly more likely to be older, female, and overweight or obese. Children with T2-high asthma were more likely to be male and non-Hispanic Black and to have vitamin D insufficiency and bronchodilator responsiveness than controls. Children with either asthma subtype were more likely to have a family history of asthma, hay fever episodes in the prior year, and lower %predicted FEV1 and FEV1/FVC than controls. In the secondary analysis, current second-hand smoke exposure was also associated with T2-low asthma.

Conclusions: Overweight was associated with T2-low asthma, while non-Hispanic Black race and vitamin D insufficiency were associated with T2-high asthma in this study of U.S. children.