Asthma Tests

Reviewed by: HU Medical Review Board | Last reviewed: November 2021

To figure out whether you have asthma, your doctor looks at your symptoms, examines you physically, and has you take tests. The most common asthma test is spirometry. Spirometry tests your lung function by measuring how much air you can exhale and how fast you can blow the air out. Other tests include:1

If your doctor is trying to figure out whether you have a condition other than asthma, they may order more tests. If the tests do not tell your doctor for certain whether you have asthma or another condition, they may try certain medicines to see if your symptoms improve or not. It may take some time for the doctor to diagnose what is causing your symptoms.

Spirometry

Spirometry is an easy breathing test for people who are at least 5 years old. It measures how well you can push air out of your lungs. This can tell doctors whether your airways are obstructed. Spirometry measures 3 main results:1

  • Forced expiratory volume in 1 second (FEV1): how much air you can forcefully exhale in 1 second
  • Forced vital capacity (FVC): the total amount of air you can forcefully exhale
  • FEV1/FVC: the percentage of your total air capacity you can forcefully exhale in 1 second

Lower FEV1 and FEV1/FVC may mean your airways are obstructed. This is a sign of asthma. If your spirometry results change a great deal over time, it may mean your asthma is poorly controlled or getting worse.2

Your doctor may ask you to perform a spirometry test for other reasons. For example, spirometry can be used to:3,4

  • Diagnose asthma based on reduced lung function
  • See if your airway obstruction improves after you take a bronchodilator drug
  • Routinely monitor your lung function
  • See how well treatments are working

Challenge tests

Sometimes, spirometry is not enough to definitely diagnose asthma. In this case, a challenge test or “bronchoprovocation” test may help. In a challenge test, you perform spirometry before and after exposing your airways to a trigger. This can help doctors determine how sensitive your airways are.4,5

The most common types of challenge tests are:5,6

  • Irritant challenge, using a trigger like perfume or smoke
  • Exercise challenge
  • Methacholine (meth-uh-koh-leen) challenge

If your lung function drops during a challenge test, that could mean you have asthma. Doctors will give you a bronchodilator after the test to open your airways back up.4

Exhaled nitric oxide test

The exhaled nitric oxide test gives your doctor an idea of your airway inflammation. Nitric oxide is a gas made in your lungs. When your airways are more irritated, there is more nitric oxide in the air you exhale. During the test, you exhale into a machine for 10 seconds. It then measures the amount of nitric oxide in your breath.4,5

Doctors will not use this test alone to diagnose or monitor asthma. It is only used to get information when other tests are not conclusive. This test also may be helpful when trying to determine what type of asthma you have.2

Allergy tests

Your doctor may also perform allergy tests or send you to an allergist for testing. This may include skin prick tests or blood tests. Allergy tests can help identify allergens and allergic triggers that worsen your asthma symptoms. A few of the more common allergens include pollen, mold, dust mites, pet dander, and cockroaches.2

However, a positive allergy test does not always mean the allergen causes your asthma. Your doctor will also look at your health history and see if there are patterns in the symptoms you experience. If both the allergy test and your medical history confirm that an allergen is a trigger for your asthma, you can take steps to avoid that substance.2

Tests for other conditions

Sometimes it can be hard to distinguish asthma from other breathing problems. Many asthma symptoms are also symptoms of other conditions. An accurate diagnosis can be even harder for people with another condition that affects breathing.5

Some conditions make asthma harder to manage, such as inflammation of the sinuses (sinusitis) and gastroesophageal reflux disease (GERD). This is why your doctor may test you for these conditions.4

Some tests that your doctor may perform to rule out or diagnose other conditions include:4,5,7

  • Chest and sinus x-rays
  • Acid reflux assessment, which might include an esophagram, upper endoscopy, or esophageal manometry
  • Examination of phlegm in your lungs

It is important to get an accurate diagnosis so your asthma and any other health conditions you have can be treated properly.

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