Methacholine Challenge Test, Bronchial Provocation Test
In the methacholine challenge test, your lung function is measured after you inhale methacholine, a chemical that causes the bronchial tubes to constrict; in some cases, the test is performed after inhalation of other allergy-causing substances (allergens). By simulating conditions that may cause asthma symptoms and assessing how your airways react, this test can help to diagnose asthma or to identify whether inhalant allergens provoke a reaction.
Purpose of the Methacholine Challenge Test
- To identify bronchial hyperresponsiveness in people who have normal results on standard pulmonary function tests
- To diagnose mild asthma in some atypical cases, such as persistent cough
- To diagnose occupational (workplace) asthma caused by certain dusts or chemicals
- To help determine the risk of developing asthma, evaluate asthma severity and assess response to asthma treatment
- To evaluate the effectiveness of asthma medications and determine the risk for developing asthma in the future
Who Performs Methacholine Challenge Test
- A physician
Special Concerns about Methacholine Challenge Test
- Because this test carries a risk of provoking severe airway obstruction, it should not be performed in people who are known to have severe asthma or chronic lung disease.
- The presence of a recent or ongoing chest infection, an upper airway infection, or another respiratory disease may affect the test results.
Before the Methacholine Challenge Test
- Be sure to inform your doctor of all medications you are currently taking. Certain drugs, particularly bronchodilators, may affect the results and should be discontinued before the test.
- Tell your doctor if you have recently had a cold or other viral infection, or any shots or immunizations, since the test’s results might be affected.
- Do not smoke or consume products containing caffeine—such as coffee, tea, chocolate, and cola drinks—for 6 hours before the test.
- Avoid exercise or exposure to cold air for 2 hours before the test.
- If you have dentures, you will wear them during the test.
- Wear loose clothing that won’t inhibit your breathing.
What You Experience during Methacholine Challenge Test
- First, standard pulmonary function tests are done to establish your pre-test lung function.
- A clip is placed on your nose to prevent air from passing through your nostrils, and you are asked to seal your lips tightly around a mouthpiece that is attached to monitoring equipment.
- You will be asked to inhale aerosolized methacholine through a nebulizer (a device that emits an extremely fine spray for deep penetration of the lungs) for about 2 minutes. Then, after a 30-second wait, you exhale forcefully through the mouthpiece.
- If occupational asthma is suspected, potential allergens from your workplace may be used in subsequent tests.
- Pulmonary function tests are then repeated to assess how your airways reacted to these substances.
- In some cases, these tests may be performed again with higher concentrations of methacholine or allergens.
- If at any point you feel tired or lightheaded, ask for a chance to rest between test cycles.
- This procedure may take from 1 to 2 hours.
Risks and Complications of Bronchial Challenge Test
- This test may trigger a mild asthmatic episode. Bronchodilator medications are kept available for immediate treatment.
After the Methacholine Challenge Test
- You may resume any medications that were withheld before the test.
- You may experience wheezing or coughing for 30 to 60 minutes after the procedure. You may need to use a bronchodilator to relieve these symptoms.
Results of Methacholine Challenge Test
- The doctor will calculate how much methacholine or allergen it takes to produce a 20% fall in your lung function. The result is compared to normal values for healthy and asthmatic populations.
- Because abnormal airway sensitivity to methacholine (bronchial hyperresponsiveness) may be present in disorders other than asthma, such as chronic obstructive pulmonary disease, your doctor must correlate the test results with your history and symptoms before making a diagnosis.
- Based on the test results and clinical findings, your doctor will decide whether to prescribe asthma medication or to adjust your current treatment.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media