Wednesday January 18 2017
Tests for asthma aren't 100% accurate
"The great asthma myth: A third of those diagnosed don't have the condition," reports the Mail Online.
A study in Canada found about one-third of adults diagnosed with asthma in the past five years showed no signs of the condition on retesting.
Asthma has become a common condition, and can cause serious illness or death if not treated. But symptoms come and go, meaning it's not always easy to diagnose reliably.
This study found people whose asthma could not be confirmed, despite a recent diagnosis, were less likely to have had objective tests of their lung function.
About one-third were able to safely stop taking asthma medicines under medical supervision.
In the UK, guidelines recommend doctors use spirometry tests in patients with symptoms that might be asthma when the doctor is not sure. A spirometer is a device that measures how much air you can breathe out of your lungs.
New guidelines on the best tests for asthma are being developed, but doctors are currently advised to start patients on treatment right away if there is a high likelihood of asthma based on their symptoms.
If you're not sure whether you need to continue taking asthma medication, talk to your GP.
It's not advisable to cut down asthma medicine or stop it suddenly without medical supervision, as asthma attacks can be serious.
Read more about asthma.
Where did the story come from?
The study was carried out by researchers from the University of Ottawa, the University of British Columbia, the University of Manitoba, the University of Toronto, Université de Montréal, the University of Calgary, McMaster University, Dalhousie University, the University of Alberta and Université Laval, all in Canada.
It was funded by the Canadian Institutes of Health Research.
The study was published in the peer-reviewed Journal of the American Medical Association (JAMA).
The Mail Online criticised doctors for diagnosing asthma "without doing the proper tests", and repeated claims made last year that inhalers were being "dished out like fashion accessories".
However, spirometry is not a definitive test for asthma. It can miss cases (a false negative result) or suggest someone has asthma when they don't (a false positive).
Doctors are therefore currently advised to use their clinical skills as well as tests.
What kind of research was this?
This cohort study recruited adults with a recent diagnosis of asthma and tested them repeatedly for asthma.
Researchers took people with no signs of the illness off medication and followed them for a year to see what happened. They also investigated how the patients had been diagnosed.
Cohort studies can find patterns – such as a link between asthma tests at diagnosis and the result of later retesting – but cannot prove that someone who didn't have a spirometry test at diagnosis did not have asthma, for example.
What did the research involve?
Researchers contacted thousands of people from 10 Canadian cities, asking if they'd had a diagnosis of asthma in the past 10 years.
Those who had and agreed to take part in the study were given a series of tests to confirm their diagnosis.
People whose tests didn't show signs of asthma were assessed by a lung specialist. Those who still had no signs of asthma had their medication reduced over time and, if appropriate, stopped.
They were then followed up for a year to see whether their symptoms worsened, and had two asthma tests during the year.
The first asthma test was spirometry, which measures how much air people can breathe out in one second. The test is then repeated after taking a puff from an asthma inhaler to see if that improves the results.
If it does, this indicates people have reversible airflow obstruction (reversible by medication), a key sign of asthma. If people had a negative spirometry test, they went on to further tests.
The researchers used a bronchial challenge test, in which people breathe in a chemical called metacholine that causes the airways to narrow. They then had spirometry to see how much the airways are affected at different doses.
If people did not have signs of asthma on this test, they had their dose of asthma medicine halved and were then retested after three weeks.
If those tests were normal, they stopped taking medicine altogether and were tested after another three weeks.
People who had no signs of asthma on any test then saw a lung specialist to look for an alternative diagnosis, and were followed up with two further bronchial challenge tests after 6 and 12 months.
Researchers also contacted the doctors who'd diagnosed the people in the study and asked about the process they'd used, whether they'd ordered spirometry or other tests, and for the results of those tests.
The researchers analysed the results to see how many of the people in the study could have a diagnosis of asthma ruled out. They also looked for differences between people with and without confirmed asthma.
What were the basic results?
Of the 1,026 people eligible to take part in the study, 613 completed all the study assessments and had their diagnosis of asthma either confirmed or ruled out.
- In total, 410 (67%) people had their diagnosis of asthma confirmed and 203 (33%) had asthma ruled out.
- Only a third of people who had asthma ruled out were taking asthma medication on a daily basis, though 79.3% were taking asthma medication occasionally.
- Half of those with a confirmed diagnosis used asthma medication daily and 90% occasionally.
- Only 86 people had their asthma confirmed by the initial spirometry test. Some (28) weren't diagnosed by tests at all, but had their diagnosis confirmed by a specialist at the final consultation.
- Alternative diagnoses for the 203 people who'd had asthma ruled out included rhinitis and acid reflux. But 61 people (27%) had no symptoms of breathing trouble at all. Twelve people had serious cardiovascular conditions that had been misdiagnosed.
- People whose diagnosis was ruled out were more likely to have been diagnosed without undergoing spirometry tests than people whose diagnosis had been confirmed. Just 43.8% of people whose diagnosis was ruled out had undergone airways tests at diagnosis, compared with 55.8% of people whose diagnosis was confirmed.
How did the researchers interpret the results?
The researchers say their results show that either people were misdiagnosed, or their condition had got better between diagnosis and retesting.
They say the test results, including follow-up results, show asthma symptoms and test results do come and go.
However, the researchers say the study suggests that "misdiagnosis of asthma may occasionally occur in the community".
They say 24% of doctors didn't answer requests for information about diagnosis of their patients, so it's "impossible to determine whether the initial diagnostic workup [initial assessment by their doctor], and hence the initial diagnosis of asthma in these participants, were appropriate".
This means we don't know to what extent the results were down to diagnosis or natural fluctuations in asthma symptoms.
The study results show being diagnosed with asthma at one point in your life doesn't necessarily mean you need to take asthma medication forever.
This study has some limitations. It was carried out in Canada, where the health service is different and doctors may use different practices to diagnose asthma. That means we don't know if the results are applicable to the UK.
Also, many people invited to take part did not do so, which means the participants may not be representative of the general population of people with asthma.
Not all doctors provided records of diagnosis, so we don't know how many people actually had asthma tests.
A third of people without asthma were not taking daily medication anyway, which indicates that they did not have current symptoms of asthma.
UK guidelines suggest people should have their need for asthma medication checked regularly so they don't take more than they require to keep symptoms under control.
Some people may be able to decrease their doses and then stop taking medication completely with medical supervision.
But it's not something you should do without your doctor's advice, as asthma attacks can be dangerous.
While tests like spirometry can help doctors make a diagnosis, they're not foolproof.
The National Institute for Health and Care Excellence (NICE) is currently looking at its advice on the diagnosis of asthma, and is expected to make new recommendations about the use of tests.
At present, spirometry is recommended for all people presenting with possible asthma. However, a normal result does not rule out asthma.
Further lung function tests, such as peak expiratory flow, are recommended to confirm the diagnosis and for monitoring purposes.
If you're unsure whether your asthma medication is helping or you don't know whether you need to take it anymore, talk to your GP.
They can ask you about your symptoms, offer tests, and help you decide how best to manage your condition.
Read more about living with asthma.