Asthma: Steps in testing and diagnosis

Updated: 2024-01-25

An asthma diagnosis is based on several factors, including a detailed medical history, a physical exam, your symptoms, and overall health and test results.

Medical history

The first step in diagnosing asthma is talking to your healthcare team about your symptoms and your health. This can provide clues as to whether asthma or something else is causing your symptoms. Your care team will likely ask about your symptoms and your exposure to substances that have been linked to asthma. Questions might include:

• What are your symptoms? When do they occur? What, if anything, seems to trigger them?
• Are you often exposed to tobacco smoke, chemical fumes, dust or other airborne irritants?
• Do you have hay fever or another allergic condition?
• Do you have blood relatives, such as a parent, aunt, grandparent or cousin, with asthma, hay fever or other allergies?
• What health problems do you have?
• What medications or herbal supplements do you take?
• What is your occupation?
• Do you have pet birds, or do you raise pigeons?

Physical exam

Your healthcare professional may:

• Examine your nose, throat and upper airways.
• Use a stethoscope to listen to your breathing. Wheezing — high-pitched whistling sounds when you breathe out — is one of the main signs of asthma.
• Examine your skin for signs of allergic conditions such as eczema and hives.

Your healthcare professional will want to know whether you have common symptoms of asthma, such as:

• Recurrent wheezing.
• Coughing.
• Trouble breathing.
• Chest tightness.
• Symptoms that occur or worsen at night.
• Symptoms that are triggered by cold air, exercise or exposure to allergens.

Asthma symptoms in children

In children, additional symptoms may signal asthma. These may include:

• Louder or faster than usual breathing.
• Frequent coughing or coughing that worsens after active play.
• Coughing, clear mucus and a runny nose caused by hay fever.
• Frequent missed school days.
• Limited participation in physical activities.

Tests

Spirometer

Spirometer

A spirometer is a diagnostic device that measures the amount of air you're able to breathe in and out and its rate of flow.

Your healthcare professional may use several tests to check how well your lungs are working.

Spirometry

This is the main test doctors generally use to diagnose asthma in people 5 years or older.

To help determine how well your lungs are working, you take a deep breath and forcefully breathe out into a tube connected to a spirometer. This records both the amount of air you exhale and how quickly you exhale. If certain measurements are below usual for a person your age, it may mean that asthma has narrowed your airways.

After taking lung test measurements, you may be asked to inhale an asthma drug to open air passages and then do the test again. Showing significant improvement after taking the medicine could mean you have asthma.

Challenge test

If your spirometer results are typical or near typical, your healthcare professional might try to trigger asthma symptoms. This is done by having you breathe in a substance that causes the airways to narrow in people with asthma, such as methacholine (meth-uh-KO-leen).

If you appear to have asthma triggered by exercise, called exercise-induced asthma, you may be asked to do physical activity to see whether it triggers symptoms.

After either action, you'll retake the spirometry test. If your spirometry measurements remain typical, you probably don't have asthma. But if your measurements have fallen significantly, it's possible you do.

Lung tests in children

Lung tests in children under age 5 are not typically done. Instead, diagnosis is generally based on a child's symptoms, medical history and physical examination. It can be especially difficult to diagnose asthma in young children because there are many conditions that cause asthma-like symptoms in this age group.

If your child's healthcare professional suspects asthma, your child may be prescribed a bronchodilator — a drug that opens the airways. If your child's symptoms improve after using the bronchodilator, your child may have asthma.

Exhaled nitric oxide test

You breathe into a tube connected to a machine that measures the amount of nitric oxide gas in your breath. Nitric oxide gas is produced by the body usually, but high levels in your breath can mean that your airways are inflamed — a sign of asthma.

Additional tests: Ruling out conditions other than asthma

If your healthcare professional suspects that you have a condition in addition to or other than asthma, you may need tests such as:

• X-ray or computerized tomography (CT) imaging of your chest.
• CT scans of your sinuses.
• Blood tests.
• Gastroesophageal reflux assessment.
• Testing of the phlegm in your lungs for signs of a viral or bacterial infection.

Your care professional also may want to see whether you have other conditions that often happen with asthma and can worsen symptoms. These include:

• Heartburn, also known as gastroesophageal reflux disease or GERD.
• Hay fever.
• Sinusitis.

Your healthcare professional also may perform allergy tests. These can be skin tests, blood tests or both. Although not used to diagnose asthma, allergy tests can help identify an allergic condition, such as hay fever, that may be causing your symptoms or worsening existing asthma.

Sometimes, diagnosing the cause of breathing problems is a challenge. It can be difficult to tell asthma from other conditions — particularly in young children.

When asthma happens with another condition that affects breathing, it can further complicate diagnosis.

Even if a diagnosis isn't certain, your care professional may prescribe medicines or other treatment to see what helps. It may take time — and patience — to get the correct diagnosis and decide on the best course of treatment.