Overdiagnosis of asthma in obese and nonobese adults

Abstract

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.

Figure 1: Algorithm used for serial testing to confirm or exclude asthma in participants using inhaled corticosteroids or leukotriene receptor antagonists on entry into the study. *Negative result of bronchial challenge test = the dose of methacholine at which the forced expiratory volume in 1 second (FEV₁) fell by at least 20% was greater than 8 mg/mL.

Figure 2: Selection of participants and study outcomes.

Figure 3: Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for determinants of an overdiagnosis of asthma among obese and nonobese adults in whom asthma had been diagnosed by a physician. Adjustments were made for clinically relevant discriminators such as baseline FEV₁, age at diagnosis of asthma, sex and daily use of asthma medication before entering the study.

Figure 4: Adjusted ORs and 95% CIs for environmental exposures associated with an overdiagnosis of asthma among obese and nonobese adults in whom asthma had been diagnosed by a physician. Adjustments were made for high-risk occupation (firefighter, farmer, painter, mechanic or construction worker), exposure to fumes, dusts, pets and cigarette smoke.