Up to one-third of adults newly diagnosed with asthma might not have the disease, a Canadian study presented at ATS2016 has suggested.
Dr Shawn Aaron from the University of Ottawa told the ATS meeting that very high rates of lifetime diagnosis had been reported in some Canadian provinces.
“It is unclear whether physicians are properly investigating and correctly diagnosing asthma,” he said.
With his colleagues, he commissioned random-digit phone dialling to recruit 701 adult non-smoking adults from 10 communities who said they had been diagnosed with asthma in the past five years.
They obtained information from their diagnosing doctor to determine how the diagnosis of asthma was originally made, and assessed the patients with spirometry, home peak flow and symptom monitoring and repeated bronchial challenge tests while being tapered off asthma medications over four study visits.
A diagnosis of current asthma was excluded if they did not have an acute worsening of asthma symptoms, reversible airflow obstruction or bronchial hyper-responsiveness despite being entirely weaned off asthma medications.
If the diagnosis was excluded, patients were carefully reviewed by a respiratory physician to establish a potential alternative diagnosis, and they were followed for a year with repeated methacholine challenge tests at 6 and 12 months.
Full information was available for 613 patients, of whom only 382 (62%) had asthma confirmed by the study team. Of the 231 who did not appear to have asthma after the initial investigations, there were 28 who had asthma confirmed over the next year when reviewed by a specialist.
The most common alternative explanations for their symptoms were rhinitis and gastro-oesophageal reflux disease.
“Importantly, some significant diagnoses were missed when symptoms were mistakenly attributed to asthma, including ischaemic heart disease, pulmonary hypertension and interstitial lung disease” Dr Aaron said.
“Misdiagnosis leads both to inappropriate asthma treatment, and lost opportunities to address other undiagnosed conditions.”
Only half the patients had spirometry or methacholine challenge performed in the community to confirm the diagnosis.
“We conclude that asthma is improperly worked up in the community and is over-diagnosed in about 30% of adult North Americans,” he said.