A methacholine challenge test is also known as bronchoprovocation test. This means that lungs are provoked to react to a chemical to see if the lungs are hyper-reactive. The test is done to assess how “reactive” or “responsive” the lungs are to things in the environment. A methacholine challenge test is designed to help doctors evaluate symptoms that point to asthma such as chest tightness, shortness of breath, and cough.
During the test, you will inhale doses of methacholine, a chemical that can cause narrowing of the airways, similar to what asthma patients experience. A breathing test is repeated after each dose in order to measure the degree of narrowing of the airways caused by this chemical.
The test will start with a very small dose of methacholine. Depending on the response, doses will be increased until the patient experiences a 20 percent drop in breathing ability or the patient reaches a maximum dose with no noticeable change in lung function.
What to Expect During a Methacholine Challenge Test
Several hours or days before the test, your doctor might ask you to stop some of your inhalers. This is done so it does not interfere with the test. In addition, your doctor will ask you not to consume products that contain caffeine like tea, soda, or coffee, at least four hours before the test.
A breathing test called spirometry will be performed to establish a baseline. After the breathing test, you will receive a very small dose of methacholine through a nebulizer. It is possible that you will experience chest tightness or cough. It is also possible that you will not experience or manifest any symptoms at all.
You will then be asked to repeat the breathing test to evaluate further constriction or narrowing of your airways. Depending on the results, you may be given a second dose of nebulized methacholine at a higher concentration. This will be followed by another breathing test.
Once you start experiencing any discomfort like increased shortness of breath or wheezing, or if the breathing test indicates a significant narrowing of the airways, the test will be ended.
Understanding Your Methacholine Challenge Test Results
The methacholine challenge test is considered positive if the methacholine causes a 20 percent (or greater) decrease in your breathing ability when compared to the baseline. A positive test will suggest that your airways are “reactive,” and a diagnosis of asthma will be considered. A negative test on the other hand means an asthma diagnosis is unlikely.
Methacholine Challenge Test Risks
While the methacholine challenge test is considered very safe, it can cause tightening of the airways or bronchoconstriction. It is also possible that you will experience common symptoms of an asthma attack like coughing, shortness of breath, wheezing, and chest tightness.
The test may also make you feel uncomfortable or dizzy but you will be watched closely. If the test indicates that there is constriction of the airways, you will be provided a bronchodilator to relieve the symptoms. There are specific conditions in which the methacholine challenge test should not be performed, including:
- If you register a very low lung function during the baseline spirometry test
- If you have had a stroke or heart attack the last three months
- If you have uncontrolled high blood pressure
- If you have aneurysm in your brain or aorta
- If you are pregnant or nursing
The staff that will perform the test will first look into your medical history before the test. Be sure to inform them if you have any of the above conditions, if you have increased cough or cold, or if you are feeling unwell on the day of the test.