A third of asthma patients may not actually have the disorder, according to new research published Tuesday in the Journal of the American Medical Association (JAMA).

The researchers surveyed 613 randomly-selected asthma patients who were receiving treatment across Canada. They found that 203 of the patients – 33 percent of the survey – didn’t have the condition and were needlessly taking medications. Of the patients whose medical records could be accessed, the researchers found half had not been properly tested before being diagnosed.

If someone has asthma-like symptoms, they may seek a physician to determine the cause, said Shawn Aaron, an asthma doctor at the Ottawa Hospital Research Institute who led the study. These signs can include wheezing, chronic airway obstruction and shortness of breath, but they are not always asthma.

“Without any testing, a physician might say ‘gee that sounds like asthma, here, take this inhaler,’” Aaron continued, but that’s not the way things should go.

Medical guidelines call on doctors to request a spirometry report, which confirms how well a patient’s lungs are working, rather than simply relying on reported symptoms. These tests should happen before doctors hand out prescriptions, based on these guidelines.

“But there are no regulations,” Aaron said. “Doctors ultimately have a lot of power to practice the way they want to.”

Misdiagnosis, however, may not shoulder all the blame. Some of the survey patients may have had asthma that has since become inactive, but they have continued taking medicine.

Canadian and American asthma treatment guidelines suggest that doctors reassess their patients’ symptoms periodically. If a patient’s asthma symptoms are under control, the physician could taper down treatment.

“But in reality most doctors are not doing this,” Aaron said. Aaron himself admits to being part of group. Sometimes physicians assume that if a patient isn’t having health problems, their treatment must be working.

Overdiagnosis, which occurs in a variety of medical fields, can have lasting negative impacts for asthma patients. For example, a Nova Scotia woman had to go to the emergency room after feeling fatigued and experiencing dangerously low blood pressure. Doctors discovered that her asthma treatment –inhaled steroids–had shut off her adrenal glands. She had never taken the appropriate tests to validate her asthma diagnosis.

That story “highlights one of the side effects — that [these drugs] can suppress your own natural ability to make these hormones,” said Brian Christman, an asthma doctor at Vanderbilt University who was not involved in the study. “Although these medicines have a great safety records, they’re not entirely benign.”

Aaron and Christman both cited convenience as a reason that doctors skip spirometry reports before prescribing asthma medication. However, Aaron notes, it would be considered absurd for a diabetes doctor to prescribe medication without clinically confirming the disorder.

Of the surveyed patients who had an asthma diagnosis without active asthma, a third had nothing wrong with them at all. Two percent had serious health conditions like heart disease or pulmonary hypertension, and 65 percent had minor health conditions like allergies.

Christman and Aaron agree that asthma medication is critically important and has saved many lives. But the new study highlights the prevalence of misdiagnoses.