Methacholine Challenge Test

What is the Methacholine Challenge Test?

The methacholine challenge test (MCT) is a specialized lung function test used to help diagnose asthma. Methacholine is a medication that, when inhaled, causes the airways to temporarily narrow, similar to what happens during an asthma attack.
During the test, doctors measure how your lungs respond to increasing doses of methacholine to determine if your airways are unusually sensitive.

Why Is the Methacholine Challenge Test Done?

Doctors typically order a methacholine challenge test when:

• Asthma is suspected, but regular breathing tests (like spirometry) appear normal
• A patient has symptoms such as coughing, wheezing, chest tightness, or shortness of breath with no clear cause
• The provider needs to confirm or rule out bronchial hyperresponsiveness, which is a key feature of asthma
  
  

This test helps confirm a diagnosis of asthma or eliminate other possible lung conditions.

Before the Test

• Your doctor may ask you to stop certain medications (like bronchodilators or antihistamines) for a specific period before the test
• Avoid smoking and strenuous activity the day of the exam
• Do not eat a heavy meal beforehand

Your healthcare provider will give you clear instructions to ensure accurate and safe testing.

During the Test

The test is done in a medical facility under the supervision of trained staff.

You will first perform a baseline spirometry test to measure your normal lung function. You’ll then inhale increasing doses of methacholine mist through a nebulizer. After each dose, you’ll perform another spirometry test. The test continues until you show signs of airway narrowing (a significant drop in lung function) or reach the maximum dose with no reaction. If your lung function decreases, you’ll be given a bronchodilator to quickly open your airways.

The entire procedure usually takes about 1 to 2 hours.

After the Test

Most patients recover within minutes after receiving the bronchodilator.

You’ll be monitored until your breathing returns to normal. You can typically resume your usual activities after the test unless instructed otherwise.

Your doctor will review the results with you and explain the next steps

The methacholine challenge test is generally safe and well-tolerated when performed under medical supervision. However, because the test intentionally narrows the airways, you may temporarily experience:

• Coughing
• Wheezing
• Shortness of breath
• Chest tightness
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These symptoms are usually mild and reversed quickly with a bronchodilator. Serious reactions are rare, and staff are trained to respond immediately to any complications. The test is not recommended for individuals with very low lung function, severe asthma, or certain heart conditions.