As many as one third of adults diagnosed with asthma may not actually have the disease, a Canadian study suggested Tuesday.
The study, published in the Journal of the American Medical Association, looked at 613 randomly selected patients from 10 Canadian cities diagnosed with asthma in the last five years.
After a series of detailed breathing tests followed by consultation with a lung specialist, asthma was ruled out in 203, or 33 percent, of these patients.
After an additional 12 months of follow-up, 181 participants, or 30 percent, continued to exhibit no clinical or laboratory evidence of asthma.
The researchers speculated that the failure to confirm a previous diagnosis of asthma by doctors could be because of spontaneous remission or misdiagnosis.
"It's impossible to say how many of these patients were originally misdiagnosed with asthma, and how many have asthma that is no longer active," lead author Shawn Aaron, senior scientist and respirologist at Ottawa Hospital and professor at the University of Ottawa, said in a statement.
"What we do know is that they were all able to stop taking medication that they didn't need -- medication that is expensive and can have side effects."
According to the study, 80 percent of the participants who did not have asthma had been taking asthma medication, and 35 percent took it daily.
The study also found that doctors often did not order the tests needed to confirm an asthma diagnosis. Instead they based their diagnosis solely on the patient's symptoms and their own observations.
"We need to educate physicians and the public to get the diagnosis right in the first place," said Aaron. "Asthma can be deadly, so patients should never go off their medication without speaking to a doctor first."
Diagnosis of asthma can be difficult because various types have been identified, all of which potentially have different triggers and symptoms.
Asthma can be episodic or can follow a relapsing and remitting course, which further complicates attempts to arrive at a diagnosis based on a single patient-physician encounter.