Methacholine Challenge Test
What Is the Procedure?
Methacholine challenge test (also known as bronchoprovocation test) is performed to evaluate how "reactive" or "responsive" your lungs are to things in the environment. It can help your doctor evaluate symptoms suggestive of asthma, such as cough, chest tightness and shortness of breath, and help diagnose whether or not you have asthma. During the test, you will be asked to inhale doses of methacholine, a drug that can cause narrowing of the airways, similar to those seen in asthma. A breathing test will be repeated after each dose of methacholine to measure the degree of narrowing or constriction of the airways. The test starts with a very small dose of methacholine and, depending on your response, the doses will be increased until either you experience 20 percent drop in breathing ability, or you reach a maximum dose with no change in your lung function.
What to Expect
Your doctor will review your current medications and ask you to stop some of your inhalers several hours or days before the procedure to prevent any interference with the test. Also, your doctor will ask you not to consume any products with caffeine, such as coffee, tea or soda, for at least four hours before the test. You will first be asked to perform a breathing test (spirometry) to establish a baseline. Following this, you will receive methacholine through a nebulizer at a very small dose.
You may experience cough or chest tightness, but most patients do not experience any symptoms. You will be asked to repeat the breathing test to evaluate for any narrowing or constriction of your airways. Depending on these results, you may receive a second dose of nebulized methacholine at a higher concentration, followed by another spirometry test.
When you start to experience discomfort, such as wheezing and increased shortness of breath, or the breathing test demonstrates significant narrowing of the airways, your doctor will end the test.
Understanding the Results
The challenge test is considered positive if methacholine causes a 20 percent or greater decrease in your breathing ability when compared to your baseline. A positive test suggests that your airways are "reactive," and a diagnosis of asthma should be considered. A negative test means a diagnosis of asthma is unlikely.
What Are the Risks?
Although the test is very safe, it can cause bronchoconstriction, or tightening of the airways. Rarely, you may experience symptoms of an asthma attack, such as chest tightness, coughing, wheezing or shortness of breath. The test may make you feel dizzy or uncomfortable, but the pulmonary function technologist performing the challenge will watch you closely. If the test results show that there is constriction of your airways, you will be given a bronchodilator to relieve your symptoms.
There are certain conditions in which the challenge test should not be performed, including the following:
- Very low lung function on baseline spirometry test
- Heart attack or stroke in the last three months
- Uncontrolled high blood pressure
- Aneurysm of the aorta or in your brain
- Pregnancy or nursing
The testing center staff will review your medical history before the test. Please let them know if you have any of the above conditions, or if you have a cold, increased cough or feel unwell on the day of the test.
Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel. Last reviewed May 31, 2017.