What is a methacholine challenge test?

A methacholine challenge test evaluates your lung function and the reactivity (narrowing or tightening) of your airways. It helps diagnose and monitor asthma, a chronic lung disease marked by acute flare-ups of inflammation and swelling of the airways in the lungs.

A methacholine challenge test is a type of bronchoprovocation test, which measures lung function after exposure to factors that commonly trigger wheezing and other asthma symptoms. A methacholine challenge test involves inhaling a mist that contains methacholine, a substance that causes lung constriction in people with asthma. 

A methacholine challenge test is only one method to diagnose asthma. Discuss all of your testing methods with your doctor to understand which options are right for you.

Other procedures that may be performed

Your doctor will likely recommend one or more other pulmonary or lung function tests to diagnose asthma and monitor your condition. Other pulmonary function tests include:

  • Arterial blood gas test to measure oxygen and carbon dioxide levels and other factors in the blood 
  • Body plethysmography to determine how much air is present in your lungs when you take a deep breath and how much air is left in your lungs after you exhale as much as you can. A methacholine challenge test and other pulmonary function tests can be done at the same time as a body plethysmography using the same equipment.
  • Lung diffusion capacity to measure how well oxygen moves into your blood from your lungs
  • Other bronchoprovocation tests to measure lung function after exposure to factors that commonly trigger asthma. These tests use exercise, cold air, or histamine to trigger lung constriction and wheezing. 
  • Peak expiratory flow to measure the speed of exhaling and lung constriction. People with asthma use this test routinely to monitor their asthma control at home.
  • Pulse oximetry to measure oxygen levels in the blood
  • Spirometry to measure the amount of air and the rate that you inhale and exhale

Why is a methacholine challenge test used? 

Your doctor may recommend a methacholine challenge to diagnose asthma if you have with some or all of the following symptoms: 

  • Chest tightness
  • Persistent cough, especially at night or in the early morning
  • Shortness of breath
  • Wheezing or a high pitched whistling sound made when you breathe

Not all people with these symptoms have asthma. There are other conditions that have similar symptoms, and sometimes asthma-like symptoms can occur briefly without a serious underlying disease. A methacholine challenge test helps determine if your symptoms are due to asthma.

A methacholine challenge test is generally not the first test your doctor will use to diagnose your symptoms. Your doctor may consider the test when other tests, such as spirometry, have not diagnosed or ruled out asthma. Doctors also use methacholine challenge tests to evaluate asthma-like symptoms triggered by occupational, environmental or toxic exposures.  

Who performs a methacholine challenge test?

A pulmonary function technologist, supervised by a doctor, performs a methacholine challenge test. A pulmonary function technologist is trained to perform lung function tests. These tests help diagnose and monitor asthma, chronic obstructive pulmonary disease (COPD), and other breathing problems. 

The following specialists supervise methacholine challenge tests:

  • Allergist-immunologists specialize in caring for people with allergies, asthma, and other diseases of the immune system.
  • Pediatric allergist-immunologists specialize in caring for children from infancy through adolescence with allergies, asthma, and other diseases of the immune system.
  • Pulmonologists specialize in the medical care of people with breathing problems and diseases and conditions of the lungs.
  • Pediatric pulmonologists specialize in the medical care of infants, children and adolescents with diseases and conditions of the lungs.

How is a methacholine challenge test performed?