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Asthma May Be Overdiagnosed

Canadian patients may be getting treatments they don't need

November 18, 2008

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Asthma may not been nearly as common as doctors think it is. A new research study, led by Ottawa researcher Dr. Shawn Aaron, suggests that the condition may be over-diagnosed by up to 30 per cent in Canadian adults.

The study, published in the November 18, 2008 edition of the Canadian Medical Association Journal, examined 496 people from eight Canadian cities who reported receiving a diagnosis of asthma from a physician.

When the individuals were retested using the accepted clinical guidelines, it was found that 30 per cent had no evidence of asthma. Two thirds of these individuals were able to safely stop taking asthma medications.

"Our study suggests that there may be a substantial over-diagnosis of asthma in Canadian adults," said Aaron, a Senior Scientist at the Ottawa Health Research Institute and Head of Respiratory Medicine at The Ottawa Hospital and the University of Ottawa. "This is a serious issue because asthma medications are expensive and they can have side effects. Also, an inappropriate diagnosis of asthma may obscure the true cause of a patient's symptoms."

The original goal of the study was to determine if obese people were more likely to be misdiagnosed with asthma, but the results showed that misdiagnosis was just as common in people of normal weight.

The prevalence of asthma in Canada and the United States is five per cent overall, and 10 per cent for obese people. The overall prevalence has nearly doubled in the last 20 years.

"Asthma is a chronic disease that impacts people's quality of life. Because of the increasing number of cases, researchers have been examining diagnostic procedures to ensure that asthma is not being over-diagnosed and over-treated," said Dr. Peter Liu, Scientific Director of the Canadian Institutes of Health Research Institute of Circulatory and Respiratory Health.

Previous research has suggested that asthma is often diagnosed by family physicians solely on the basis of symptoms, despite the fact that clinical guidelines recommend using a spirometer to objectively measure lung volume and airway flow. A spirometer costs a few thousand dollars and can be set up fairly easily in any clinic.

"The message for patients is that if you've been diagnosed with asthma and you have not had a spirometry test, you should ask your physician for one," said Aaron. "The other important message is that asthma can be deadly, so you should never stop taking a medication without consulting a physician."

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