What is a methacholine challenge test?

The methacholine challenge test, also known as a bronchial challenge test, is a medical test that is used to assist in the diagnosis of asthma. Methacholine is a type of drug that you inhale that causes slight narrowing of the airways in the lungs, similar to asthma. This testis usually performed by a respiratory specialist.

The test can take place in your doctor’s office and the visit normally lasts around one hour.

What happens during the test?

The test begins with a baseline breathing test, known as spirometry, in order to check how well your lungs are working. During the test, you will be asked to inhale and fill your lungs with air. Then, a mouthpiece is placed between the lips and you will need to exhale with full force for at least six seconds.

This process is usually repeated at least three times, during which the methacholine is administered in increasing doses. After each new dose, a new spectrometry is made.

The test ends when your lung function drops by 20% or more compared to the previous baseline or if the maximum dose of methacholine is used. On completion of the test, you will be given specific medication to open your lungs and undergo another breathing test to ensure your lungs are working properly before you leave.

If you receive a positive result, it confirms that you have asthma. The test is considered positive if the methacholine causes your lung function to drop below 20% compared to your initial baseline result.

Preparing for the test

Before taking the test, your doctor will ask you to stop taking certain types of medications and inhalers in order to achieve a valid and accurate result. Usually, your doctor will ask you not to consume any caffeinated food and drinks such as tea, coffee, and chocolate, but you should ask your doctor about exercising before the test.

Also, you must tell the doctor if you are pregnant or suffering any heart problems. Similarly, if you have received any recent vaccinations or not feeling well you should inform your doctor.

What do you feel during the exam?

This test should not cause any discomfort, however, since you will be blowing fast using full force, you might experience some degree of light-headedness, dizziness, chest pain or shortness of breath. Always let the specialist carrying out the test know if you are feeling uncomfortable or in pain.

After the test

After the test, you can start taking your usual medications, again unless your doctor gives you other instructions, and go back to your normal activities and diet.