Asthma is a chronic lung condition that affects breathing. To diagnose asthma, a doctor may assess symptoms and use a range of breathing tests to measure lung function.

Breathing tests can help a doctor see how well the lungs are working and determine whether a person’s symptoms are due to asthma or another condition.

In this article, we look at the different tests a doctor may use to diagnose asthma and what people can expect during testing.

A person doing a spirometry test for asthma.Share on Pinterest
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Asthma is a long-term lung condition that makes moving air through the airways more difficult. There are a few types of asthma, including:

Asthma can affect anyone at any age. Most people who have asthma receive a diagnosis at a young age, but older adults can also develop asthma.

Asthma can cause wheezing, tightness in the chest, or coughing. People may find that certain factors trigger or worsen their symptoms, such as cold air, exercise, or allergens.

An asthma attack can occur if symptoms are severe. Asthma attacks can also lead to hospitalization and, in some cases, respiratory failure and death.

Asthma can cause the airways to swell and narrow. The airways can also become sensitive to environmental triggers, which may cause further inflammation and excess mucus production. This makes it difficult to breathe and causes the symptoms of asthma.

To diagnose asthma, a doctor may first take a full medical history. This may include asking questions about:

  • medications
  • lifestyle
  • occupation
  • previous medical conditions
  • history of allergies or eczema, which may increase the likelihood of having asthma
  • family history of asthma, allergies, or eczema
  • exposure to environmental triggers, such as pollen, dust, or tobacco smoke

A doctor will also ask about any symptoms that may indicate asthma, such as:

A doctor may want to know how frequently people experience symptoms, when they occur and what seems to trigger them, and whether symptoms wake people at night.

A doctor may then carry out a physical exam, which may involve:

  • listening to breathing and checking the airways
  • checking the skin for allergic conditions, such as eczema
  • checking various body parts, such as the ears, eyes, and nose

A doctor may then carry out a series of lung function tests to check for asthma. Lung function tests show how well the lungs are working and can include:


During a spirometry test, people will breathe in and out of a tube that connects to a computer. Spirometry measures the amount and speed of air people are breathing in and out.

Spirometry with bronchodilator

If a spirometry test shows reduced lung function, people may take a bronchodilator, which is a medication that opens the airways.

People will then repeat the spirometry test. If the results show improved lung function, the person likely has asthma.

Lung plethysmography

During this test, a machine measures lung volume. Lung plethysmography is also called body or pulmonary plethysmography.

A doctor may suggest this test to check if there are any other issues, such as emphysema or restriction caused by lung scarring or musculoskeletal problems.

Nitrogen washout test

This test measures the anatomical dead space in the lungs, where the air is not exchanged. The test is also known as Fowler’s method.

A person inhales pure oxygen and then exhales through a nitrogen analyzer.

A doctor may also suggest this test to check if there are any other lung problems.


A bronchoprovocation test shows how muscles in the airways react under exposure to certain substances, such as allergens or medications.

One type of bronchoprovocation test is the methacholine challenge. People will inhale a possible trigger agent, such as methacholine or mannitol, and then take a spirometry test to check the response of the airways.

A healthcare professional increases the triggering agent incrementally until they see a response or pass the anticipated threshold.

Peak expiratory flow (PEF)

A PEF test measures the speed at which people can blow air into a tube using maximum effort.

Fractional exhaled nitric oxide (FeNO)

A FeNO test measures the amount of nitric oxide that people exhale. People will breathe out into a handheld device. High levels of nitric oxide can indicate lung inflammation.

Exercise tests

If people have any asthma symptoms during exercise, they may have exercise-induced asthma or exercise-induced bronchospasm.

A doctor will conduct exercise tests to check how the body responds to extra exertion.

People may use an exercise bike or treadmill while attached to a heart monitor and blood pressure machine. While people exercise, these machines will measure vital signs.

Allergy tests

If people have a history of allergies, or if a doctor suspects an allergy could be causing or worsening symptoms, they may carry out a range of allergy tests.

Allergy testing may include blood tests or skin prick tests. Allergy tests show which allergens cause an immune reaction.

Other tests

If a doctor suspects that anything other than asthma may be causing symptoms, they may carry out additional tests to rule out other conditions.

These may include:

Diagnosing asthma in children under the age of 6 years can be more difficult. This is because younger children may not be able to take certain lung function tests, such as spirometry.

If a doctor suspects a child has asthma after assessing symptoms and medical history, they may prescribe asthma medications to see how the child responds.

Many of the initial tests for asthma can take place in a doctor’s office. According to the American Lung Association, asthma tests do not cause any pain.

People may feel a slight scratch or pricking from a needle if they have a blood test or skin prick allergy test.

A doctor may ask people to repeat the tests several times to ensure an accurate diagnosis.

Many lung function tests require people to breathe in and out through a piece of equipment. An exercise test may require people to use a treadmill or exercise bike.

The American Lung Association suggests people prepare for asthma tests by:

  • continuing to take any usual medication up until testing, unless a doctor instructs otherwise
  • avoiding smoking for at least 6 hours before any testing
  • avoiding using an inhaler for 6–8 hours before testing
  • wearing loose, comfortable clothing and suitable shoes for an exercise test
  • following any preparation advice from a doctor

After testing, people will be able to resume their normal activities.

Doctors categorize asthma into four different levels depending on the severity of symptoms and lung function.

To diagnose someone’s asthma level, a doctor may want to know how frequently people experience symptoms and whether coughing or difficulty breathing wakes them at night.

A doctor may also ask if everyday activities cause any breathing problems or if people ever need to use a rescue inhaler.

The four levels of asthma are:

  • Intermittent asthma: People experience symptoms less than twice a week and less than two nights per month.
  • Mild persistent asthma: People experience symptoms 2 days per week or more and wake in the night three or four times per month.
  • Moderate persistent asthma: People experience symptoms every day and wake at night one or more times per week.
  • Severe persistent asthma: Symptoms affect people every day and every night.

A doctor will take a person’s age, height, and gender into account when calculating normal measurements from an asthma test.

If people have any abnormal results from a test, it may indicate a lung problem. In some cases, people with healthy lung function can still have an abnormal result from a breathing test.

A doctor will interpret the results and then explain what they mean. Test results could show asthma or another condition that affects the airways.

There is currently no cure for asthma, but a treatment plan can help people manage their symptoms.

A treatment plan can include taking asthma medications, making lifestyle changes, and avoiding any triggers where possible.

To diagnose asthma, a doctor will assess symptoms, perform a physical exam, and check medical history.

A range of breathing tests can show how well the lungs are functioning and help a doctor diagnose asthma. Other tests, such as X-rays and allergy tests, can help a doctor rule out other conditions that may be causing symptoms.

If tests indicate asthma, a person can discuss a treatment plan with their doctor.