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AsthmaMarch 8, 2004
After evaluating a "gold standard" set of tests recommended by international guidelines to confirm a diagnosis of asthma, researchers from New Zealand showed that a simple measurement of exhaled nitric oxide in patients was clearly superior to currently used objective methods to diagnose the disease. A test called induced sputum analysis also gave superior results but was deemed much more technically demanding, and not routinely available.
The investigators studied 47 patients with symptoms suggestive of asthma, using a comprehensive, fixed sequence of standard diagnostic tests. (Bronchial asthma has a prevalence of about 20% in young adults in Western populations, according to the authors.) The researchers checked the sensitivities and specificities for peak flow measurements, spirometry and changes in certain airway parameters after a trial use of steroid.
These results were compared with exhaled nitric oxide measurements and sputum cell counts. The authors said that the sensitivities for each of conventional tests ran from 0-47%. These results were considerably lower than for exhaled nitric oxide measurements that ran 88%, along with 86% for sputum eosinophil analysis. (Exhaled nitric oxide increases in patients with bronchial asthma.)
Overall, the diagnostic accuracy of the exhaled nitric oxide and sputum analysis was significantly greater. The investigators noted that it is much more logical to use exhaled nitric oxide as a surrogate test for airway inflammation than to rely on physiological changes for which the measurements are variable over time, are often undetectable in mild cases, and correlate poorly with clinical symptoms.
The study appears in the American Journal of Respiratory and Critical Care Medicine (Smith AD, Cowan JO, Filsell S. Diagnosing asthma: comparisons between exhaled nitric oxide measurements and conventional tests. 2004;169:473-478). This article was prepared by Health & Medicine Week editors from staff and other reports.
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