What Is the Procedure?        

Methacholine challenge test (also called the bronchoprovocation test) is done to assess how “reactive” or”responsive” a patient’s lungs would be to things in the environment. It can help you as a doctor evaluate symptoms suggestive of asthma, such as cough, chest tightness, shortness of breath, and help diagnose whether you have asthma. During the challenge test, the patient is asked to inhale doses of methacholine, leading to narrowing of the airways, very similar to those found in asthma. A breathing test will be repeated following each methacholine dose to gauge the amount of narrowing or constriction of the airways. The trial begins with a tiny quantity of methacholine. Based on the patient’s reaction, the doses will be raised until they experience a 20 percent fall in breathing capacity or reach a maximum amount with no change in their lung function.

What to Expect

Before the test, you will examine the patient’s current medications. You may ask the patient to stop some of your inhalers several hours or days before the procedure to avoid any interference with the exam. You will also instruct them not to drink coffee, tea, or soda for a few hours before the challenge. Before beginning the methacholine challenge, the patient will first carry out a breathing test (spirometry) to establish a baseline. Following this, they will get methacholine through a nebulizer at a really small dose.

The patient may experience cough or chest tightness during the methacholine challenge, but most don’t experience any symptoms. They will be asked to repeat the breathing test to assess for any narrowing or constriction of your airways. Based on those results, the patient might be given another dose of nebulized methacholine in a higher concentration, followed by another spirometry test.

When the patient begins to experience discomfort, like wheezing and increased shortness of breath, or the breathing test demonstrates substantial narrowing of the airways, the challenge test is considered complete.

Understanding the Results

The challenge test is deemed positive if methacholine induces a 20 percent or greater breathing capacity reduction compared to the baseline. A positive test suggests the patient’s airways are”reactive,” and a diagnosis of asthma should be considered. A negative test usually means a diagnosis of asthma is not likely.

What Are the Risks?

Even though the test is extremely safe, it can lead to bronchoconstriction, or tightening of the airways. Rarely, patients might experience symptoms of an asthma attack, such as chest tightness, coughing, wheezing, or shortness of breath. The test may cause them to feel dizzy or uneasy, but the pulmonary function technologist performing the challenge will watch them carefully. If the test results show that there’s constriction of the airways, the patient should be given a bronchodilator to relieve their symptoms.

There are certain conditions where the challenge test should not be performed, including the following:

Very low lung function on a baseline spirometry test
Heart attack or stroke in the past three weeks
Uncontrolled high blood pressure
Aneurysm of the aorta or brain
Childbirth or Nursing

Before scheduling a methacholine challenge, the patient’s medical history should be reviewed. If they have any of the above conditions, if they have a cold, increased cough, or don’t feel well on the exam day, the test should not be performed.

Joyce Laroche