The challenges of diagnosing asthma

Asthma is a chronic disease of the airways that causes inflammation and narrowing of the airways, causing symptoms such as tightness in the chest, breathlessness and wheezing. Unfortunately, it’s a condition that often goes misdiagnosed or undiagnosed. Pulmonologist Dr Edward Nash talks about the different tests used to diagnose asthma and the challenges faced when making a diagnosis.

Up to 50% of asthma cases are misdiagnosed. This is because asthma can present with various symptoms such as breathlessness, wheezing and coughing that are similar to those of other conditions, such as COPD (chronic obstructive pulmonary disease), an umbrella term used to describe progressive lung diseases like emphysema and chronic bronchitis.

Asthma can also be more difficult to diagnose in children because a child might present with symptoms similar to a cold or viral bronchitis, with symptoms of wheezing and coughing. It can take a long time for asthma to become diagnosed, often taking several weeks or months, taking longer depending on when the patient presents with their symptoms.

What tests are used to diagnose asthma?

There are three main areas that doctors look at to make a diagnosis; a patient’s medical history and lifestyle factors, physical examination and investigations such as breathing tests.

Medical history and lifestyle

Your doctor will look at your history of symptoms and if there is a family history of asthma, then the patient is more likely to develop the condition. The patient will be asked if they smoke, as smoking can induce symptoms similar to asthma and they will be asked general lifestyle questions about exercise for example. Some types of asthma are only exercise-induced. A person’s occupation may also bring about or worsen asthma, particularly in the patient works with cleaning products, air conditioning or close to a swimming pool.

Breathing tests

The three main tests used to diagnose asthma are a routine breathing test called spirometry, peak flow recording and FeNO (fraction of exhaled nitric oxide).

Spirometry: this test measures how much air you can breathe out and how quickly you are able to blow it out. The patient takes a deep breath and exhales into a tube connected to a device called a spirometer. The test measures if the airways are narrowed resulting in the obstruction characteristic of asthma and COPD. However, since it is a variable condition, people with asthma don’t always have airflow obstruction on spirometry so this cannot be used to rule out asthma.

Peak flow recording: this test again measures how quickly you are able to blow air out of your lungs. The patient may be required to perform this test at home over several days or weeks. This is to try to detect the variability in airflow that is characteristic of asthma and is a more sensitive way of diagnosing asthma than spirometry.

FeNO: the new NICE guidelines recommend that this be done as a routine procedure to diagnose asthma, unfortunately, the equipment needed for this is quite expensive and many doctors can’t afford access to it. It shows how inflamed your airways are by measuring the amount of nitric oxide in your breath.

Physical examination

The doctor will routinely listen to the sounds produced by breathing and particularly listen out for any wheezing.

Sometimes blood tests will be carried out, particularly to test for allergic asthma caused by an allergen such as animal hair or pollen. There are two main blood tests used:

A blood test to check for the presence of a blood cell called eosinophils, which is the body’s allergic white blood cell. If levels of this white blood cell are raised, this suggests that the body has been exposed to an allergen and can suggest allergic asthma.

IgE test; this blood test looks for elevated levels of an antibody called IgE and not only shows if asthma is caused by an allergen, but can be used to unveil the specific allergen that is triggering asthma, such as animal hair and pollen.

However, some tests won’t work on specific types of asthma, such as non-allergic asthma. A test performed to test for the presence of eosinophils or IgE will show up as normal in 40% of cases for anyone with asthma that is not triggered by an allergen. Spirometry tests can also appear normal as asthma symptoms can vary several times a day and from day to day. A peak flow diary may be required to diagnose asthma if there is persisting doubt.

Is it helpful to think of asthma as a group of distinct diseases?

Yes, previously all types of asthma were lumped under one condition, however, it is now increasingly recognised that there are several distinct types, depending on the underlying cause. There can be:

Allergic asthma; asthma induced by a specific allergen like dust, pollen or pet hair

Infective asthma; these people are prone to bacterial infections and may often need antibiotics

Exercise-induced; asthma arises predominantly after exercising, giving rise to breathlessness and wheezing

Aspirin-induced asthma; non-steroidal anti-inflammatory drugs like ibuprofen can cause symptoms of asthma. These drugs can disrupt the inflammatory pathways in the lungs, causing the airways to narrow

Occupational asthma; triggered by specific allergens in relation to a person’s place of work.

Will there ever be a single test to confirm the presence of asthma?

It’s doubtful that there will ever be a single test, as there are so many different subgroups of people with asthma. It often takes at least three of four tests to give an accurate diagnosis, with non-allergic asthma being particularly difficult to diagnose. Sometimes doctors will suggest a ‘trial’ of an inhaled medication to assess for an improvement in symptoms and this approach can be useful if there is doubt about the diagnosis.

If you suffer from asthma or would like to know what triggers your asthma symptoms, then get in touch with Dr Edward Nash.