Exhaled nitric oxide as a screening test for asthma in children
Exhaled NO is known to be elevated in patients with asthma and may reflect airway inflammation. We wish to examine if increased levels of exhaled NO could be used as an initial screening test for asthma in children. Methods: We measured exhaled NO in 155 children aged 8-9 years and then classified them as normal (non - asthmatic, non- atopic), asthmatic, atopic asthmatic or atopic on the basis of the ISAAC questionnaire (Asher MI et al. ERJ 1995). Parents who answered 'yes' to the question 'has your child ever had asthma', 'wheeze or dry cough at night apart from cough associated with cold or chest infection in last 12 months' were classified as asthmatic. Those who were defined to have seasonal allergic rhinitis or eczema from the questionnaire were classified as atopic. All children came from the Oxfordshire town of Abingdon, were born in 1991 and 1992 and registered with a specific GP practice. Exhaled NO measurements were made over a 2 weeks period in July, and parents completed the ISAAC questionnaire within 1 week of the measurements. Exhaled NO was measured using a single exhalation method (Model LR2000, Logan Research, UK). All children exhaled at a rate of 75 ml/sec with mouth pressure maintained at 10 cm H2O. Results: All but 13 parents returned the questionnaire. Four children were not able to perform the exhaled NO measurements adequately. From the ISAAC questionnaire, 26 of 138 children were classified as asthmatics, 36 were atopic and the rest non-atopic and non asthmatics. The atopic subjects (with or without asthma) had significantly greater levels of exhaled NO levels compared to normal subjects (Mann Whitney Rank Sum Test). There was no significant difference in exhaled NO levels between asthmatic and atopic subjects. Non - atopic Atopic Asthma No asthma Asthma No asthma normal) N 6 55 20 36 NO 5.5 5.2 14.5* 6.4* I.Q 4.9-6.4 4.0-6.7 5.8-24.1 4.7-10.9 Range *significantly higher levels compared to normal ; p<0.05 Conclusion: We found no significant difference in exhaled NO levels between non asthmatic, atopic children and those with asthma. High exhaled NO levels do not appear to discriminate between atopy and asthma, and therefore is unlikely to be useful as an initial screening test for asthma.