Asthma Diagnosis and Tests

Your doctor will use tests to diagnose asthma. Some measure how well your lungs work. Others can tell if you’re allergic to mold, pollen, or other things.

All of these asthma tests help your doctor decide if you have asthma and other conditions that often come with it, like allergies, GERD, and sinusitis.

Physical Exam

Your doctor will start with a physical exam. They will:

They’ll also ask you about signs of asthma such as:

Medical History

Next, your doctor will ask about your symptoms and overall health to figure out if asthma or something else is causing your problem. Some questions might include:

  • What are your symptoms?
  • When do you have them?
  • What seems to trigger them? What about cold air, exercise, or allergies?
  • Do you have hay fever or allergies?
  • Does a family member have hay fever, asthma, or allergies?
  • What other health problems do you have?
  • What medications do you take?
  • Do you often come into contact with tobacco smoke, pets, dust, or chemicals in the air?
  • What do you do for a living?

Lung Function Tests

These asthma tests see how well your lungs work. Some of the most common used to diagnose asthma include:

  • Spirometry. This simple breathing test measures how much air you blow out and how fast. It’s often used to know the amount of airway obstruction you have.
  • Methacholine challenge. Your doctor might have you do this if your symptoms and spirometry test don’t clearly show you have asthma.
  • Peak flow . Peak flow tests measure how well your lungs push out air. Although they are less accurate than spirometry, they can be a good way to test your lungs at home -- even before you feel any symptoms. You use a small device called a peak flow meter for the test. It can help you know what makes your asthma worse, whether your treatment is working, and when you need emergency care.
  • Exhaled nitric oxide test. You’ll breathe into a tube connected to a machine that measures the amount if nitric oxide in your breath. Your body makes this gas normally, but levels could be high if your airways are inflamed.


Chest X-Ray

While a chest X-ray isn’t an asthma test, your doctor can use it to make sure nothing else is causing your asthma symptoms. An X-ray is an image of the inside of your body created by using low doses of radiation. By viewing an X-ray of your lungs, your doctor can see if asthma is likely to be causing your symptoms.


Nasal polyps or sinusitis may make asthma harder to treat and control. Sinusitis, also called a sinus infection, is an inflammation or swelling of the sinuses due to infection. When the sinuses become blocked and filled with fluid, bacteria grow, causing infection and inflammation. Your doctor may order a special sinus X-ray, called a CT scan, to examine your sinuses if they think you have an infection. If you have sinusitis, you will be treated with antibiotics for at least 10 to 12 days. Treating the sinusitis may help prevent asthma symptoms.

Tests for Other Conditions

The doctor may also do tests for other conditions that can make asthma worse, like:

  • Gastroesophageal reflux disease, or GERD
  • Allergies

Judging the Severity of Asthma

Based on these tests and your symptoms, your doctor may diagnose you with asthma. The next step is to find out if your asthma is severe. This will help them decide your treatment. You’ll have one of these four types of asthma:

  1. Mild intermittent asthma. Mild symptoms less than twice a week. Nighttime symptoms less than twice a month. Few asthma attacks.
  2. Mild persistent asthma. Symptoms three to six times a week. Nighttime symptoms three to four times a month. Asthma attacks might affect activities.
  3. Moderate persistent asthma. Symptoms every day. Nighttime symptoms five or more times a month. Asthma attacks affect your activities.
  4. Severe persistent asthma. You have ongoing symptoms both day and night. They’re so frequent that you have to limit your activities.

If doctor diagnoses you with asthma, they can prescribe asthma medications to help manage your condition and prevent attacks.

WebMD Medical Reference Reviewed by Carol DerSarkissian on April 29, 2019



The Canadian Lung Association: "Signs and Symptoms of Asthma: Diagnosis."

National Jewish Medical and Research Center: "How Is Asthma Diagnosed?"

American College of Allergy, Asthma & Immunology: "About Asthma: Diagnosing Asthma."

Mayo Clinic: “Asthma: Steps in testing and diagnosis.”

Medscape: “Asthma Guidelines.”

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