CMAJ • November 18, 2008; 179 (11). doi:10.1503/cmaj.081332.
© 2008 Canadian Medical Association or its licensors
All editorial matter in CMAJ represents the opinions of the authors and not necessarily those of the Canadian Medical Association.
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Research

Overdiagnosis of asthma in obese and nonobese adults

Shawn D. Aaron, MD, Katherine L. Vandemheen, BScN, Louis-Philippe Boulet, MD, R. Andrew McIvor, MD, J. Mark FitzGerald, MD, Paul Hernandez, MD, Catherine Lemiere, MD, Sat Sharma, MD, Stephen K. Field, MD, Gonzalo G. Alvarez, MD, Robert E. Dales, MD, Steve Doucette, MSc, Dean Fergusson, PhD for the Canadian Respiratory Clinical Research Consortium

From the Ottawa Health Research Institute (Aaron, Vandemheen, Alvarez, Dales, Doucette, Fergusson), University of Ottawa, Ottawa, Ont.; the Centre de recherche (Boulet), Hôpital Laval, Université Laval, Laval, Que.; the Firestone Institute for Respiratory Health (McIvor), McMaster University, Hamilton, Ont.; the Department of Medicine (Fitzgerald), University of British Columbia, Vancouver, BC; the Department of Medicine (Hernandez), Dalhousie University, Halifax, NS; the Department of Medicine (Lemiere), Université de Montréal, Montréal, Que.; the Department of Medicine (Sharma), University of Manitoba, Winnipeg, Man.; and the Department of Medicine (Field), University of Calgary, Calgary, Alta.

Correspondence to: Dr. Shawn Aaron, Division of Respiratory Medicine, Department of Medicine, The Ottawa Hospital – General Campus, 501 Smyth Rd., Ottawa ON K1H 8L6; fax 613 739-6266; saaron{at}ohri.ca

Background: It is unclear whether asthma is overdiagnosed in developed countries, particularly among obese individuals, who may be more likely than nonobese people to experience dyspnea.

Methods: We conducted a longitudinal study involving nonobese (body mass index 20–25) and obese (body mass index ≥ 30) individuals with asthma that had been diagnosed by a physician. Participants were recruited from 8 Canadian cities by means of random-digit dialing. A diagnosis of current asthma was excluded in those who did not have evidence of acute worsening of asthma symptoms, reversible airflow obstruction or bronchial hyperresponsiveness, despite being weaned off asthma medications. We stopped asthma medications in those in whom a diagnosis of asthma was excluded and assessed their clinical outcomes over 6 months.

Results: Of 540 individuals with physician-diagnosed asthma who participated in the study, 496 (242 obese and 254 nonobese) could be conclusively assessed for a diagnosis of asthma. Asthma was ultimately excluded in 31.8% (95% confidence interval [CI] 26.3%–37.9%) in the obese group and in 28.7% (95% CI 23.5%–34.6%) in the nonobese group. Overdiagnosis of asthma was no more likely to occur among obese individuals than among nonobese individuals (p = 0.46). Of those in whom asthma was excluded, 65.5% did not need to take asthma medication or seek health care services because of asthma symptoms during a 6-month follow-up period.

Interpretation: About one-third of obese and nonobese individuals with physician-diagnosed asthma did not have asthma when objectively assessed. This finding suggests that, in developed countries such as Canada, asthma is overdiagnosed.




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