Diagnosis of asthma.

A significant weakness of the excellent work by Kaplan and colleagues relates to a lack of discussion on the spirometric overlap between asthma and chronic obstructive pulmonary disease (COPD) and how this may lead to disease misclassification. This clarification is important since their diagnostic algorithm for asthma, Figure 1, contains a decision node labelled “Spirometry results consistent with asthma” referring to improvements in forced expiratory volume in one second (FEV1) after bronchodilator challenge; changes that can also be seen in many patients with COPD. It is also important to provide clarification about what is meant by “reversibility of airflow obstruction” as this applies to asthma and COPD. It could be argued that airflow obstruction defined by a reduction in the ratio of FEV1 and forced vital capacity (FVC) is irreversible in COPD since, by definition, it must remain below some predetermined value after bronchodilator challenge. However, a persistent reduction in FEV1/FVC after bronchodilation in COPD may be associated with significant changes in airway calibre (FEV1) similar to that recommended for the spirometric diagnosis of asthma. Furthermore, the FEV1/FVC may remain reduced after bronchodilator challenge in asthma; highlighting the spirometric overlap that may exist between asthma and COPD in terms of FEV1 and FEV1/FVC changes after bronchodilator challenge. Therefore, COPD can be characterized by a persistent reduction in FEV1/FVC after bronchodilation irrespective of airway calibre changes. For spirometric diagnoses of asthma, criteria for changes in airway calibre must be met irrespective of the FEV1/ FVC value; the latter is often normal in asthmatics. This information is not clearly apparent in the diagnostic algorithm for asthma, Figure 1, and could result in disease misclassification in some patients.