Dear Editor,

Berkman and colleagues [1] put forward an impressive argument for the use of exhaled nitric oxide (eNO) in diagnosing asthma through employment of a cut off value of 7 parts per billion in differentiating between asthmatics and non-asthmatics.

Although it is unquestionable that elevated levels of eNO indicate underlying airway inflammation, it must be appreciated that the latter is not synonymous with asthma. The same can be said of a positive response to bronchial provocation, which merely signifies the presence of bronchial hyperresponsiveness but not necessarily asthma.

I am slightly perturbed to note the presence of a clear outlier within the asthma group as evidenced from the scatter plots in Figure 1(A). This is especially pertinent as eNO is the primary outcome variable in a study consisting of a relatively small number of patients where any outlier may be potentially confounding. Can the authors provide reassurance that the results of the study still hold true when the solitary outlier is excluded from data analysis?

eNO is at present best suited as a tool for monitoring response to anti-inflammatory therapy in asthma. eNO can also be useful in aiding a clinician in diagnosing asthma when considered in conjunction with other measures of airway inflammation. However, to utilise eNO as a sole diagnostic test for asthma may be premature without first embarking on further definitive studies.

References

1. Berkman N, Avital A, Breuer R, et al. Exhaled nitric oxide in the diagnosis of asthma: comparison with bronchial provocation tests. Thorax 2005;60:383-8.