Asthma: Steps in testing and diagnosis

Date Updated: 06/04/2026

By Mayo Clinic Staff

An asthma diagnosis is based on a review of symptoms and medical history, a physical exam, and test results.

Symptoms and medical history

Your healthcare professional will likely ask you several questions about symptoms, the time and place of symptoms, daily activities and medical history. Be prepared to answer these questions about your experience or to answer them on behalf of your child.

Questions about breathing. Your healthcare professional will likely ask you questions about current or recent breathing symptoms:

Can you hear a whistling sound or wheezing while breathing?
Do you ever find it hard to breathe or catch your breath?
Have you had chest tightness or pain?
Have you had a cough?

Questions about the time or place of symptoms:

Do the symptoms come and go?
Do breathing troubles or a cough wake you up or keep you awake?
What time of day do symptoms happen?
Are symptoms worse at certain times of the year?
Do you have symptoms after exercising?
Where are you when you have symptoms or when symptoms get worse — home, school, work or somewhere else?

Questions about other factors related to asthma:

Do you have symptoms when you're around pets?
Do you have allergies? Is there a history of asthma or allergies in your family?
Have you had a cold, the flu or other illness recently?
Do you smoke or vape? Are you around secondhand smoke?
Are you exposed to chemicals, fumes, smoke or other irritants?
Do you get heartburn? Do you ever have a bitter or acidic taste in your mouth?
What recreational activities and hobbies do you do regularly?
What medicines, herbs or supplements do you take?

Questions about the impact of symptoms:

Have you missed school or work because of symptoms?
Have you had emergency room visits for these symptoms?
Do you avoid activities because of symptoms?

Physical exam

Your healthcare professional will likely:

Look inside your nose and throat.
Listen to your lungs while you're breathing in and out.
Examine your skin for signs of allergic conditions, such as a rash.
Measure your heart rate and temperature.

Lung function tests

Your healthcare professional may use one or more tests to see how well the lungs are working. Test for lung function are usually not done on children younger than age 5.

Spirometry

This is the main test for diagnosing asthma. The test device is called a spirometer. It measures how much air you breathe in, how much you breathe out and how quickly you breathe out. The results show how much your breathing is limited. The results are recorded as:

Forced vital capacity (FVC). This is the largest amount of air that you can forcefully breathe out after breathing in as deeply as you can. An FVC reading that's lower than what's typical means your breathing is limited.
Forced expiratory volume (FEV). This test shows how much air you can force out of your lungs. An FEV-1 result shows how much air you can force out in one second. Asthma makes it particularly difficult to breathe out. This reading helps your healthcare professional figure out how serious your breathing trouble is. Lower FEV-1 readings mean greater blockages in the airways.

The test may be repeated after you take an inhaled medicine that relaxes the muscles around the airways. Better spirometry results after taking the medicine help confirm an asthma diagnosis.

Challenge test

This test may be used when symptoms suggest asthma, but spirometry test results don't support a diagnosis.

With a challenge test, a spirometry test is done after exposure to something that can trigger an asthma attack. The spirometry test is then repeated to see if there is improvement after taking a quick-acting asthma medicine to open the airways. The results can help confirm a diagnosis of asthma.

A challenge test may be done with:

An inhaled medicine.
Exercise.

FeNO test

FeNo stands for fractional concentration of exhaled nitric oxide. This test measures nitric oxide when you breathe out. Nitric oxide is released by white blood cells, called eosinophils. Eosinophils are part of a complex immune system response called inflammation.

Typically, inflammation helps fight disease. But with asthma, long-term inflammation is the underlying condition that leads to swelling, tightened muscles and excess fluids. These reactions narrow airways in the lungs and make it hard to breathe.

For a FeNO test, you breathe into a tube connected to a machine that measures the amount of nitric oxide gas in your breath. A high nitric oxide level is a sign of inflammation in the airways.

Other tests

Other tests to support a diagnosis of asthma include:

Blood test. A blood test can look for high levels of eosinophils in the blood, which can indicate inflammation.
X-ray. A chest X-ray may be done to rule out other causes of breathing symptoms.
Allergy testing. Allergy tests can be performed by a skin test or blood test. These tests help show substances that may cause an allergic reaction. Your healthcare professional may order these tests if allergic reactions are suspected triggers of asthma attacks.

Trial treatment

Your healthcare professional may do a trial treatment with an inhaled medicine that opens airways. This medicine acts quickly. A diagnosis of asthma is more likely if symptoms improve within the time the medicine is expected to work.

A treatment trial may be especially helpful for diagnosing asthma in young children who cannot do a lung test.

Severity of asthma

When making a diagnosis of asthma, your healthcare professional will judge the overall effect of the disease on breathing and the risk to your health or your child's health. This helps guide the choice of medicines, doses and other treatment decisions. Things considered for judging asthma severity include:

Number of days a week or how often during a day asthma symptoms happen.
Number of nighttime awakenings a month due to asthma symptoms.
Impact of symptoms on daily activities.
Spirometry test results.

Classification systems vary. Your healthcare professional may classify the disease as:

Intermittent.
Mild persistent.
Moderate persistent.
Severe persistent.

After making a diagnosis of asthma, your healthcare professional will prescribe treatments. Treatments are stepped up or down over time depending on how well symptoms are managed. Your health professional also works with you to develop an asthma action plan. This plan helps you decide what medicine to take, when to call your health professional and when to get emergency care.