Van Amsterdam JGC, Janssen NAH, de Meer G, et al. Clin Exp Allergy. 2003;33:187–191
Purpose of the Study.
To determine whether there is a relationship between levels of exhaled nitric oxide (eNO) and sensitization to common allergens.
A convenience sample of 450 schoolchildren (7–12 years of age), of a total random sample of 2504 children in the Netherlands, were enrolled.
Children were recruited from 7 public schools and were assessed for allergen sensitization with skin prick testing and/or specific immunoglobulin E (IgE) radioallergosorbent testing (RAST) with common environmental allergens, including dust mite, cat, tree, grass, dog, and mold allergens. eNO was measured with a standard protocol. Families were also asked to complete a questionnaire regarding the home environment, family composition, education, and passive smoke exposure. Associations between eNO levels and sensitization to common allergens were analyzed with adjustments for age, gender, gas cooking, unvented water heaters, passive smoke exposure, and having a cold during sampling.
Of the total 450 children studied, 9% had a lifetime history of asthma, with 10% reporting wheeze in the previous year, 8.2% had a history of hay fever, and 29.1% had a history of eczema ever. Of the 319 children who underwent skin prick testing, 29.5% had ≥1 positive test result, 21.9% for indoor allergens and 15% for outdoor allergens. Of the 229 children who underwent specific IgE RAST, 32.3% had ≥1 positive test result, 23.1% for indoor allergens and 21.8% for outdoor allergens. The geometric mean level of eNO was ∼1.5 times higher among children sensitized to indoor allergens, compared with nonsensitized children (P < .05), and this was increased to 2 times higher when a cutoff value of ≥2 positive tests was used for either indoor or outdoor allergen sensitivity. eNO levels gradually increased with increases in positive allergen tests. There was no association between eNO levels and current pet ownership. The association between allergen sensitization and eNO was much stronger among children with a history of wheezing, compared with children without wheezing (relative increases of 1.24–1.47 among nonwheezers and 1.56–3.44 among wheezers).
This study found a positive association between eNO levels and levels of allergen sensitivity in a random sample of schoolchildren in the Netherlands. The association was stronger among children with sensitization to indoor allergens and children with a history of wheezing. Association with sensitization to outdoor allergens was not as strong, which the authors proposed might be related to the larger particle size of pollens preventing their entry into lower airways. The mechanism of these elevated eNO levels is not known, but the authors proposed that exposure to allergens could lead to inflammatory changes in the lower airway without causing signs of clinical asthma.
The authors concluded that allergen sensitization was associated with elevated levels of eNO in a random sample of children, most without outward signs of asthma.
eNO has been shown in many studies to be a useful marker of inflammation among asthmatics, but this study demonstrated an association between atopy and eNO levels. It has been suggested that eNO may be a useful screening test for asthma, and perhaps some of these asymptomatic atopic patients are evolving asthmatics. Although eNO devices have received Food and Drug Administration approval, their cost has limited their use to research settings to date.