Department of Family Medicine (Dr. Wells) and Division of Pulmonary, Critical Care, Sleep, and Allergy Medicine (Dr. Joo), University of Illinois at Chicago. cwells2@uic.edu
The authors reported no potential conflict of interest relevant to this article.
In 2 longitudinal studies, patients with a diagnosis of asthma were recruited to undergo medication reduction and serial lung function testing. Asthma was excluded in approximately 30% of patients.15,16 Diagnostic error has also been seen in patients hospitalized with exacerbations of COPD and asthma. One study found that only 31% of patients admitted with a diagnosis of COPD exacerbation had undergone a spirometry test prior to hospitalization.17 And of those patients with a diagnosis of COPD who underwent spirometry, 30% had results inconsistent with COPD.17
In another study, 22% of adults hospitalized for COPD or asthma exacerbations had no evidence of obstruction on spirometry at the time of hospitalization.18 This finding refutes a diagnosis of COPD and, in the midst of an exacerbation, challenges an asthma diagnosis as well. Increased awareness of clinical practice guidelines, coupled with the use and accurate interpretation of spirometry are needed for optimal management and treatment of COPD and asthma.
Airflow measurement is decisive in diagnosing COPD and asthma
Clinical practice guidelines recommend spirometry for the diagnosis of COPD and asthma and have been issued by GOLD10; the American College of Physicians, American College of Chest Physicians, American Thoracic Society, and the European Respiratory Society19; the Global Initiative for Asthma (GINA)2; and the National Heart, Lung, and Blood Institute.20
When a patient’s symptoms and risk factors suggest COPD, spirometry is needed to show persistent post-bronchodilator airflow obstruction and thereby confirm the diagnosis. However, in the United States, confirmatory spirometry is used only in about one third of patients newly diagnosed with COPD.21,22 Similarly for asthma, in the presence of suggestive symptoms, spirometry is the preferred and most reliable and reproducible test to detect the variable expiratory airflow limitation consistent with this diagnosis.
An alternative to spirometry for the diagnosis of asthma (if needed) is a peak flow meter, a simple tool to measure peak expiratory flow. When compared with spirometry, peak flow measurements are less time consuming, less costly, and not dependent on trained staff to perform.23 However, this option does require that patients perform and document multiple measurements over several days without an objective assessment of their efforts. Unlike spirometry, the peak flow meter has no reference values or reliability and reproducibility standards, and measurements can differ from one peak flow meter to another. Thus, a peak flow meter is less reliable than spirometry for diagnosing asthma. But it can be useful for monitoring asthma control at home and in the clinic setting,24 or for diagnosis if spirometry is unavailable.23