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One-third of recent asthma cases may be misdiagnosed: study

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One-third of people recently diagnosed with asthma may not actually have the condition, according to a new study from Canadian researchers that raises questions about rates of misdiagnosis.

Even though the asthma of some study subjects might have gone into remission, the findings suggest many others were wrongly diagnosed, possibly because doctors did not send them for simple lung-function tests.

"It just astounds me," said Shawn Aaron, senior scientist and respirologist at the Ottawa Hospital and lead author of the study, published on Tuesday in the Journal of the American Medical Association. "Only half of the patients are getting the right testing, which sort of floors me."

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From January, 2012, to February, 2015, the researchers looked at more than 600 people in Canada's 10 largest cities and their surrounding areas who were diagnosed with asthma in the five years before they joined the study. The researchers tested patients and reduced their medication use to assess whether the diagnoses were accurate, and determined that 203 of 613 participants did not have active asthma.

After a year, the researchers found more than 90 per cent of the patients who did not have asthma were able to stay off of medication. After one year, six out of the 203 individuals had to return to medication, while another 16 had positive tests indicating asthma but did not need drugs. The rest remained well and tested negative for asthma, Dr. Aaron said.

Less than half of those diagnosed with asthma who were found not to have it, or 44 per cent, had a lung-function test called spirometry at the time of their initial diagnosis.

Spirometry involves breathing into a tube to measure lung function and is considered more reliable in the diagnosis of asthma than looking at symptoms alone. About 35 per cent of people in that group were taking asthma medication daily and 80 per cent were also taking other types of medication, the researchers found. About 56 per cent of those whose asthma was confirmed had those tests when they were diagnosed.

Aaron, who is also a professor at the University of Ottawa, likened it to going to the doctor because of frequent urination, a symptom of many conditions, including diabetes, and being diagnosed with and treated for diabetes without further tests.

"The doctor would always, always, without exception, do blood-sugar tests prior to assigning treatment," he said, adding that when it comes to asthma, "people aren't getting the right testing."

Aaron said many of the study participants who did not actually have asthma were dealing with issues such as allergies, postnasal drip, heartburn or obesity that caused symptoms that could appear similar to asthma.

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Although the lung-function test is cheap and easy to perform, health policy makers have not seen it as essential and therefore it is often difficult to access, Aaron said.

Patients may have to drive for half an hour to a hospital that can perform it, which could help explain why many patients do not have it. Instead, some doctors may prescribe treatment and, if the symptoms resolve, assume the asthma diagnosis was accurate, Aaron said.

But given that many people may be misdiagnosed, it is time for health leaders to make lung-function tests as easy to access as blood tests or X-rays, Aaron said.

Becky Hollingsworth, who lives about an hour outside Ottawa, is one of the study participants wrongly diagnosed with asthma without undergoing spirometry. She was told she had the condition after a bout of pneumonia and was taking medications to control the symptoms. She was one of the Canadians selected randomly to be part of the clinical trial, and without that, she said, she would still be receiving treatment as if she were asthmatic.

"I am very glad that the study came along and that I'm not still on asthma medication," she said.

In addition to the possibility of side effects, Hollingsworth feared her insurance rates would go up as a result of the diagnosis.

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Aaron said side effects from asthma medications can include oral thrush, rapid heart rate, tremors and, over the long-term, osteoporosis, glaucoma and cataracts. Another concern is the cost of unnecessary medication, both to an individual and to the public- and private-insurance systems. He said patients should speak to their doctors about how the diagnosis was made, and that doctors should order a spirometry test before making an asthma diagnosis.

It is difficult to say how many study participants might have been misdiagnosed with asthma versus those that had the condition but experienced remission. For instance, the researchers found that 12 per cent of study participants who were found not to have asthma did have lung-function tests at the time of diagnosis. This suggests the diagnosis was accurate, but that the patients may have experienced "spontaneous remission," according to the study authors. Another 2 per cent of those who did not have asthma actually had serious cardiorespiratory conditions.

Asthma is a chronic inflammatory disease of the airway that causes symptoms that include shortness of breath, wheezing and coughing. According to Statistics Canada, about 8 per cent of Canadians, or 2.4 million people, had asthma in 2014.

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