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OTTAWA (Reuters) - Up to 30 percent of Canadians diagnosed with asthma may not have the disease, and obese people are particularly vulnerable to misdiagnoses, according to a study released on Tuesday.
A team led by Dr. Shawn Aaron of the Ottawa Health Research Institute said doctors tempted to diagnose asthma should carry out more specialized tests such as spirometry, which involves breathing into a special machine to check lung function.
Aged-adjusted data showed that between 1980 and 1994 the number of people diagnosed with asthma had grown by 75 percent, in part due to increasing awareness by patients and their doctors, the Ottawa research team said.
But the study -- published in the Canadian Medical Association Journal -- suggests that at least part of the increase may reflect misdiagnoses.
The team carried out a six-month study of 496 obese and non-obese patients who had been diagnosed with asthma.
"We found that one-third of the participants who had received a diagnosis of asthma by a physician had no evidence of asthma when their medications were tapered and when they were evaluated with serial assessments of symptoms, lung function and bronchial challenge tests," it said.
"One obvious interpretation of this observation is that asthma was over-diagnosed in the community. Consequently, over-diagnosis and changes in diagnostic labeling may be contributing to increases in the prevalence of asthma reported in developed countries."
Asthma can be confused with other respiratory diseases as well as chronic obstructive pulmonary disease.
"There are obvious consequences associated with a misdiagnosis of asthma, including the lost opportunity to investigate or treat the cause of the patient's respiratory symptoms appropriately, the patient's potential exposure to the adverse effects of asthma medications (and) the cost of asthma medications," said the report.
The team said obese patients were particularly vulnerable to faulty diagnoses because they had asthma-like symptoms such as reduced lung volumes and increased breathing rates.
The researchers tested all 496 subjects for asthma and asked those who with no obvious signs of the disease to reduce their use of medication.
The people in this smaller group who showed no worsening of symptoms were then asked to stop taking their medications.
The study found that 32 percent of the obese and 29 percent of the non-obese patients who had been diagnosed with asthma did not have the condition.
"Physicians should consider objective testing using spirometry and, if necessary, bronchial challenge testing to confirm asthma in patients with respiratory symptoms," it said.
An accompanying article in the medical journal said almost half of those patients diagnosed with asthma were never given spirometry tests, a practice it said was unacceptable.
"A physician who attempted to manage hypertension without measuring blood pressure ... would not be considered to be maintaining an adequate standard of care. Treating asthma without having performed at least spirometry is no different," said the article.
It said those wrongly diagnosed with asthma were "needlessly exposed to possible adverse outcomes -- albeit usually minor -- and costs, which can exceed C$100 ($81) per month for a single medication."
Reporting by David Ljunggren; Editing by Frank McGurty