Asthma phenotypes, risk factors, and measures of severity in a national sample of US children.

OBJECTIVE To examine a nationally representative sample of US children aged 6 to 16 years old and determine whether there are differences in risk factors and measures of severity between children with different asthma phenotypes. METHODS We analyzed data from the Third National Health and Nutrition Examination Survey. We used questionnaire and skin-prick testing data to separate children into the following mutually exclusive categories: atopic asthma, nonatopic asthma, resolved asthma, frequent respiratory symptoms with no asthma diagnosis, and normal. We used multivariate regression to determine whether demographic or potential risk factors varied between phenotypes and whether measures of severity varied by phenotype. RESULTS We found that 4.8% of children had atopic asthma, 1.9% had nonatopic asthma, 3.4% had resolved asthma, and 4.3% had frequent respiratory symptoms. Risk factors varied by phenotype, for example, the mean BMI was higher among children with nonatopic asthma, prenatal maternal smoking was a risk factor for resolved asthma, and child care attendance was a risk factor for frequent respiratory symptoms with no asthma diagnosis. Patients with atopic and nonatopic asthma were similar for most measures of asthma severity (medication use, health status, and lung function impairment). In contrast, patients with resolved asthma had fewer symptoms but a similar level of lung function impairment to that seen in patients with current asthma, whereas children with frequent respiratory symptoms but no asthma diagnosis had normal lung function. CONCLUSIONS Asthma risk factors and measures of severity vary between children with different asthma phenotypes.