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Asthma may be over-diagnosed by up to 30 per cent, according to Canadian research study

November 17, 2008

A new research study suggests that asthma may be over-diagnosed by up to 30 per cent in Canadian adults. The study, led by Ottawa researcher Dr. Shawn Aaron, examined 496 people from eight Canadian cities who reported receiving a diagnosis of asthma from a physician. When the individuals were retested for asthma 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. The results are published in the November 18, 2008 edition of the Canadian Medical Association Journal.

“Our study suggests that there may be a substantial over-diagnosis of asthma in Canadian adults,” said lead author Dr. Shawn Aaron, a Senior Scientist at the Ottawa Hospital 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 Dr. Aaron. “The other important message is that asthma can be deadly, so you should never stop taking a medication without consulting a physician.”

This study was funded by the Canadian Institutes of Health Research.

About the Ottawa Hospital Research Institute: The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and is an affiliated institute of the University of Ottawa, closely associated with the University’s Faculties of Medicine and Health Sciences. The OHRI includes more than 1,300 scientists, clinical investigators, graduate students, postdoctoral fellows, and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease. www.ohri.ca

About the Canadian Institutes of Health Research: The Canadian Institutes of Health Research (CIHR) is the Government of Canada’s agency for health research. CIHR’s mission is to create new scientific knowledge and to enable its translation into improved health, more effective health services and products, and a strengthened Canadian health-care system. Composed of 13 Institutes, CIHR provides leadership and support to nearly 12,000 health researchers and trainees across Canada. www.cihr-irsc.gc.ca

Media contacts:
Jennifer Paterson, OHRI Media Relations
Phone: 613-798-5555 x 19691
Cell: 613-614-5253
Email: jpaterson@ohri.ca

David Coulombe, CIHR Media Relations
Phone: 613-941-4563
Email: mediarelations@cihr-irsc.gc.ca