As many as 30.2% of people diagnosed with asthma don’t have the disease, newly published research suggests.

Using spirometry and bronchial challenge tests with methacholine, researchers affiliated with the University of Ottawa tried to confirm physician diagnoses in 496 people from eight Canadian cities. Asthma was excluded in 150 subjects within four follow-up visits. Two thirds of that group were safely able to discontinue their asthma medication within six months (CMAJ. 2008;179:1121-1131).

“This is a serious issue because an inappropriate diagnosis may obscure the true cause of a patient’s symptoms,” notes lead author Shawn Aaron, MD, MSc, a senior scientist at the Ottawa Health Research Institute. “Also, asthma medications are expensive and they can have side effects.”

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An editorial by Stanbrook and Kaplan published in the same issue agrees and cautions that asthma may be misdiagnosed rather than overdiagnosed (CMAJ. 2008;179:1099-1102). Symptoms attributed to asthma may signify other underlying medical conditions. The authors agree that all suspected cases of asthma must
be diagnosed with spirometry, which should be available in all practice settings.