Asthma can be hard to diagnose. There is no test which definitively proves that a patient does or does not have it. So doctors have had to rely on their own experience and the patient’s symptoms when diagnosing. But both are subject to fluctuation and human error.

This means that as many as one million adults in the UK may have been wrongly diagnosed with asthma and are now taking unnecessary medications with potentially harmful side effects, according to an NHS watchdog.

Fortunately, as asthma testing techniques improve, incorrect diagnoses should become less common. NICE (National Institute for health Care Excellence) has written up a new set of guidelines for diagnosing asthma. They feel the first test doctors should use is spirometry.

Spirometers measure how much a person can breathe out and how fast. They are inexpensive and effective for diagnosing asthma. Plus, they can also help patients exercise their lungs and increase lung volume. When a patient breathes out, a ball is suspended in midair. So, patients simply practice keeping the ball in the air for longer and longer periods.

Experts warn that no one should stop taking asthma medication without first consulting their doctor, even if they think they’ve been wrongly diagnosed. Also, according to asthma charity Asthma UK, even though some people are wrongly diagnosed, under-diagnosis and under-treatment of asthma are both still major and very common issues. “Three people die every day because of asthma. Most of these deaths could have been avoided through better control of the disease,” said Asthma UK.