There is no single test for asthma diagnosis. Your doctor will:
- ask about the symptoms
- ask about general health, including whether you (or other family members) have allergies like eczema or hay fever etc.
- do a physical examination (e.g. listen to the chest)
- consider other possible causes of the symptoms
- arrange a spirometry test (for adults and children aged 6 years and over).
How well the lungs work (lung function) is tested using a spirometer. You blow into a tube as forcefully and as long as you can. The spirometer measures the amount of air pushed through the tube, as well as lung capacity and other parameters.
Airflow can vary in healthy people too (e.g. when someone has a cold their lungs may not work as well as usual). But people with asthma have a much bigger difference than healthy people between how their lungs work at their best and at their worst.
Most children over 6 years old can do this asthma test. If you or your child has a cold or flu, spirometry should be repeated later when you are well.
The doctor will be looking for signs of conditions that often go along with asthma such as rhinitis (inflammation of the nose), sinusitis (inflammation of the sinuses), nasal polyps (mucus-filled sacks in the nose), eczema or dermatitis (skin irritation).
Sometimes the doctor needs to do other tests:
- Allergy tests, either skin or blood
- A test to see how your airways react to exercise
- Tests for other conditions, such as gastroesophageal reflux disease (GERD) or obstructive sleep apnea
- A test for sinus disease
- A chest x-ray or electrocardiogram to check for signs of separate lung or heart disease
- Exhaled nitric oxide (FeNO) test to measure lung inflammation
What does it mean?
The doctor will look at your ears, eyes, nose, throat, skin, chest and lungs. To rule out other possible conditions — such as a respiratory infection or chronic obstructive pulmonary disease (COPD) — your doctor will ask you questions about your signs and symptoms and about any other health problems. This exam may include a lung function test to detect how well you exhale air from your lungs. You may also need an X-ray of your lungs or sinuses.
Lung Function Test
To see how well your lungs are working, how much air moves in and out as you breathe.
This is a test to confirm asthma. You will take a deep breath and then exhale forcefully into a mouthpiece that’s connected to a device, called spirometer. This test estimates the narrowing of your bronchial tubes by checking how much air you can exhale after a deep breath and how fast you can breathe out.
A peak flow meter is a simple a small, handheld device that measures how hard you can breathe out. During the test you breathe in as deeply as you can and then blow into the device as hard and fast as possible. Lower than usual peak flow readings are a sign your lungs may not be working as well and that your asthma may be getting worse. If you’re diagnosed with asthma, you can use a peak flow meter at home to help track your condition.
Lung function tests often are done before and after taking a medication called a bronchodilator, such as salbutamol/albuterol, to open your airways (reversibility test). If your lung function improves after inhaling a bronchodilator, it’s likely you have asthma.
Exhaled Nitric Oxide Testing – FeNO
We all exhale a little nitric oxide (NO). But too much nitric oxide is an indicator of lung inflammation, the underlying condition of asthma. Measuring nitric oxide levels in your breath (FeNO, or fractional exhaled nitric oxide) can be useful in testing for and monitoring asthma. The noninvasive test involves breathing into a machine that detects FeNO levels; it can easily be performed by patients of all ages.
Methacholine, when inhaled, will cause mild constriction of your airways. If you react to the methacholine, you likely have asthma. This test may be used even if your initial lung function test is normal.
Is a provocative test for exercise and cold-induced asthma. In these tests, your airway obstruction before and after you perform vigorous physical activity or take several breaths of cold air is measured.
Allergy testing can be performed by a skin test or blood test. Allergy tests can identify a wide range of allergens. If important allergy triggers are identified, this can lead to a recommendation for allergen immunotherapy.