Different Diagnostic Tests for Asthma

Diagnosing asthma is a process that involves several steps. First, your healthcare provider will ask you to describe all of your symptoms. This includes how often the symptoms occur, when they tend to happen, and if there is anything that makes them get worse. Your healthcare provider will also take your medical history and ask about any other medical conditions that you have. For example, people will allergies or a skin condition called eczema may be more likely to have asthma.^1-3

At this point, if your healthcare provider thinks that you might have asthma, then the next step is a physical examination to check out your eyes, ears, nose, throat, chest and lungs, and skin. As part of the physical exam, your healthcare provider may use some special types of diagnostic tests to help figure out if you have asthma, or whether your symptoms have some other cause.

What diagnostic tests are used for asthma?

Your healthcare provider can use several different kinds of diagnostic tests to help diagnose asthma:

• Lung function tests
• Imaging tests
• Allergy tests
• Sputum test

Lung function tests

Special breathing tests called lung function tests are used to measure the amount of air that can move in and out of your lungs as you breathe. The most common types of lung function tests for diagnosing asthma are called:^1-3

• Spirometry test
• Peak flow test
• Challenge tests
• Exhaled nitric oxide test

Spirometry test

During a spirometry test, a special machine called a spirometer is used to measure the amount and speed of air that you can breathe in and out of your lungs. The peak flow test uses a peak flow meter to measure how hard you can breathe air out of your lungs.

Peak flow test

Spirometry tests and peak flow tests are usually performed before and after taking a bronchodilator medication, such as albuterol. If the results of the test show that your lung function is better after you have taken the medicine, then it is a sign that you probably have asthma.

If the results of your spirometry and peak flow tests don’t make it clear whether or not you have asthma, then your healthcare provider may use challenge tests or an exhaled nitric oxide test to help make the diagnosis.

Challenge tests

Challenge tests are also called trigger tests. During this type of test, you will be asked to inhale a substance that is a well-known asthma trigger. If you have asthma, this substance will very likely cause you to have asthma symptoms—and you will not react to it if you don’t have asthma.

Nitric oxide test

Another test, called a nitric oxide test, is used to measure the amount of nitric oxide gas produced by your lungs. This gas is a result of inflammation in your lungs, and this kind of inflammation is a sign of asthma.

Imaging tests

Imaging tests can also help your healthcare provider to figure out if you have asthma. These tests may include an x-ray or CT scan of your lungs, sinuses, and/or heart. These tests can be used to see if your breathing symptoms might have some cause other than asthma. They can also determine if you have other conditions that may make your asthma worse.^1-3

Allergy tests

During allergy testing, a skin test or a blood test is used to see if you are allergic to things such as pet hair, mold, pollen, or dust. These tests are not used to diagnose a person with asthma, but they can be used to see if those allergies are triggering your asthma or making it worse. Allergy tests can also be used to help figure out the best way to treat your asthma.^1-3

Sputum tests

A sputum test is used to see if there are special cells called eosinophils” in the sputum (mucus) that is produced when you cough. Having a higher level of these types of cells in your sputum may be a sign of inflammation caused by asthma.¹