Methacholine Challenge Test

A methacholine challenge (bronchoprovocation test) is a breathing test healthcare providers use to help diagnose asthma. During the test, you alternate between inhaling increasing doses of methacholine and using spirometry to test your lung function. Methacholine is a drug that can make your airways narrow slightly.

If your lung function drops 20% or more below your baseline (what’s usual for you) during the test, your airways are reactive. You may have asthma.

During the test, you may cough, wheeze or feel short of breath. This is normal. If this happens, your provider will end the test and give you a bronchodilator (like albuterol) to open your airways. You should feel better within a few minutes. The test rarely causes serious breathing problems.

You shouldn’t have this test if you:

• Have very low lung function (based on prior or initial spirometry)
• Are pregnant or nursing
• Have high blood pressure that’s not well-managed
• Have a brain aneurysm
• Have had a heart attack or stroke in the last three months

Preparing for a methacholine challenge test

Your provider will give you instructions on how to prepare for the test. These may include:

• Not consuming caffeine, like coffee, tea, soda or chocolate
• Not taking asthma medications or using your inhaler for a certain amount of time before the test

Let your provider know if you’ve had a respiratory infection (like a cold, the flu or COVID-19) in the past two weeks or if you aren’t feeling well the day of the test.

You also might want to consider having someone go with you to the test. You aren’t required to have someone drive you home. But you may feel more comfortable having someone else who can drive if the test brings on asthma symptoms.

What happens during the test?

During a methacholine challenge test:

1. Your provider will get a baseline lung function level using spirometry. They’ll instruct you on how to breathe into a machine to get this measurement.
2. You’ll breathe in a dose of methacholine using a nebulizer.
3. You’ll repeat the spirometry test to measure your lung function.
4. You’ll continue alternating between inhaling increasing doses of methacholine and measuring lung function.
5. The test ends either when you reach the last dose of methacholine or your lung function drops 20% or more below your baseline.
6. After the test, your provider may give you medication that opens your airways to reverse any effects of the methacholine.

Providers do this test in a controlled and safe way, with rescue medications nearby. Let your provider know how you’re feeling throughout the test. Tell them right away if you’re experiencing:

• Dizziness
• Lightheadedness
• Shortness of breath
• Coughing
• Wheezing
• Chest pain

If your lung function gets too low or you’re having symptoms, your provider will stop the test and give you a bronchodilator to help you breathe better.

What do the results of a methacholine challenge test mean?

A positive test result means your lung function dropped 20% or more compared to your baseline. This means you have reactive airways and can suggest an asthma diagnosis. If the test is negative, it’s very unlikely you have asthma.

Contact your healthcare provider if you have any questions about how to prepare for the test or about the results.