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How does your GP diagnose asthma?

Your general/family doctor or GP will do several things to figure out if you have asthma:

  • Ask about your symptoms: The doctor will talk to you to understand how you’re feeling and what problems you’re having.
  • Ask about your medical history: Do you have family members with asthma or allergies? Are you smoking, exposed to secondhand smoke (passive smoking) or exposed to pollutants in the workplace?
  • Perform a thorough physical examination: The doctor will focus on your chest, nose, throat, ears, and eyes. For example, the doctor will listen to your chest with a stethoscope for any sounds of wheezing.
  • Test how your lungs are working: there are several breathing tests your GP or asthma nurse may perform if they have the equipment in their office to perform them. The most commonly performed lung function tests are spirometry and peak flow measurements. Spirometry tests measure the amount of air you can blow out in one forced breath. A peak flow test is performed to measure how fast you can blow air out of your lungs.
  • Checking for allergies: If allergies might be triggering your symptoms, your GP may perform a skin prick test or recommend blood testing, depending on availability.
  • In some cases, additional testing is necessary to rule out other conditions that can mimic symptoms of asthma.

When will your GP refer you to see a specialist?

How does your specialist diagnose asthma?

Specialists, like pulmonologists, may perform more advanced tests to confirm your diagnosis and find out what’s causing your symptoms. They might also repeat some of the tests already done by your GP, such as:

  • Spirometry: measures the amount of air you can blow out in one forced breath (see above). Often, the bronchodilator reversibility test (BDR) is done alongside spirometry at the specialist’s office. The combination helps your doctor determine whether your airways respond to medication—and if so, how much your lung function improves as a result.
  • Peak flow test: to measure how fast you can blow air out of your lungs (see above)
  • Check for allergies: if allergies might be triggering your symptoms, a skin prick test or blood test might be performed. Not all GP practices offer these kinds of testing (see above).

In addition to these, specialists also perform:

  • Challenge tests, like the methacholine or mannitol test, are used for asthma diagnosis to check how sensitive your lungs are compared to normal to triggers that can cause your airways to tighten or narrow.
  • Exhaled nitric oxide or FeNO test: This test measures the amount of nitric oxide in the air you breathe out. Higher levels of nitric oxide can be a sign of inflammation in your airways, which is common in conditions like asthma.
  • Blood test to measure your eosinophil levels. Eosinophils are a type of white blood cell responsible for inflammation. People who have high levels of eosinophils can have increased swelling in the airways, which can lead to asthma symptoms.
  • Oscillometry (or forced oscillation technique, FOT): This test measures lung function using gentle pressure waves while you breathe normally, for asthma diagnosis. It’s easier than spirometry because it doesn’t require deep breaths or hard blowing.
  • Induced sputum test requires you to produce a fresh sample of sputum/phlegm, which can then be analysed for different cells found in your deeper airways.

When is a CT scan considered?

Most people with asthma don’t need imaging tests, like a CT scan. However, if someone has asthma that is hard to control, especially if it’s severe asthma, a CT scan may be considered.

For people who don’t have a clear asthma diagnosis, a CT scan can help rule out other, less common conditions that can mimic the symptoms of asthma. Some patients may have another condition alongside asthma that makes their symptoms more severe. If asthma is already diagnosed and confirmed, a CT scan can sometimes help find problems like mucus build-up (also called mucus plugs) or other issues in the deeper airways. These problems lead to limited airflow and reduced lung function and are often linked to more severe asthma. 

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Overview

How does your GP diagnose asthma?
How does a specialist diagnose asthma ?
When is a CT scan considered?
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