A comparison of obese and nonobese people with asthma: exploring an asthma-obesity interaction.

OBJECTIVE: The objectives of our study were to compare patient characteristics and severity of disease in obese and normal-weight-confirmed people with asthma and to explore reasons for misdiagnosis of asthma, including potential interactions with obesity.
METHODS: We randomly selected patients with physician-diagnosed asthma from eight Canadian cities. Asthma diagnosis was confirmed via a sequential lung function testing algorithm. Logistic analysis was conducted to compare obese and normal-weight-confirmed people with asthma and to assess characteristics associated with misdiagnosis of asthma. Interaction with obesity was investigated.
RESULTS: Complete assessments were obtained on 496 subjects who reported physician-diagnosed asthma (242 obese and 254 normal-weight subjects); 346 had asthma confirmed with sequential lung testing, and in 150 subjects a diagnosis of asthma was ruled out. Obese subjects with asthma were significantly more likely to be men, have a history of hypertension and gastroesophageal reflux disease, and have a lower FEV(1) compared with normal-weight subjects with asthma. Older subjects, men, and subjects with higher FEV(1) were more likely to have received misdiagnoses of asthma. Obesity was not an independent predictor of misdiagnosis, however there was an interaction between obesity and urgent visits for respiratory symptoms. The odds ratio for receiving a misdiagnosis of asthma for obese individuals as compared with normal-weight individuals was 4.08 (95% CI, 1.23-13.5) for those with urgent visits in the past 12 months.
CONCLUSIONS: Obese people with asthma have lower lung function and more comorbidities compared with normal-weight people with asthma. Obese individuals who make urgent visits for respiratory symptoms are more likely to receive a misdiagnosis of asthma.