The methacholine challenge test is used to diagnose and manage respiratory disorders like asthma. It involves inhaling increasing doses of methacholine, which acts on airway muscle receptors to cause contraction. Spirometry is then used to measure the sensitivity of the airways. A PC20 value is calculated from the spirometry results to quantify airway hyperresponsiveness, with a value below 16 mg/mL indicating abnormal sensitivity. While the test provides information about asthma and other conditions, there are limitations like potential safety issues from induced bronchoconstriction and factors that could produce false positive or negative results.

1. Methacholine
Challenge Test
Presented By:Marij Noor

2. Table of Contents
Results Analysis
Introduction Test Mechanism
Limitations
01
03
02
04

3. • The test is used to diagnose and
manage respiratory disorders such as
asthma.
• Its purpose is to measure how sensitive
a person's airways are to an inhaled
stimulus.
Methacholine Challenge Test

5. Mechanism
• It involves the administration of methacholine, a synthetic cholinergic
agonist, via inhalation to provoke a temporary narrowing of the airways
in order to evaluate the presence and severity of bronchial
hyperresponsiveness.
• Methacholine acts on specific receptors known as muscarinic
receptors, particularly the M3 receptors, which are abundantly present
in the smooth muscle of the airways. When inhaled, methacholine
stimulates these receptors, causing smooth muscle contraction and
resulting in airway narrowing.
• The MCT typically follows a standardized protocol involving
incremental dosages of methacholine. The initial doses are relatively
low, and the concentration is gradually increased until a predetermined
endpoint is reached. The endpoint is defined by a clinically significant
decrease in lung function parameters or a specific level of airway
responsiveness.

6. • Before the test, patients need to ensure that they have not
taken any medications that may affect the test results.
• They must also avoid smoking, exercising, or eating before
the test.
• The test involves inhaling a bronchoconstrictor,
Methacholine, and measuring the response in spirometry
tests.
Pre-test preparations

7. Equipment Required
Mouthpiece
Nebulizer Methacholine
solution
Flow meter
Spirometer
1 3 5
2 4

9. Results Interpretation
• The Provocative Concentration (PC20) is a key parameter calculated
during the methacholine challenge test (MCT). It represents the
concentration of methacholine required to cause a 20% decrease in
forced expiratory volume in one second (FEV1) compared to the
baseline measurement. The PC20 is used to quantify airway
hyperresponsiveness, which is an important characteristic of conditions
such as asthma.
Interpretation of PC20:
• Normal Response: A PC20 greater than 16 mg/mL is considered
within the normal range. This indicates that the airways are not overly
sensitive or responsive to methacholine, suggesting the absence of
significant airway hyperresponsiveness.
• Abnormal Response: A PC20 of 16 mg/mL or less is considered
abnormal and indicates increased airway sensitivity and reactivity. A
lower PC20 value reflects greater airway hyperresponsiveness. This is
often seen in conditions like asthma or exercise-induced

10. False-negative
Results
Equipment calibration,
appropriate methacholine
dosing, and patient
cooperation
There is a
potential risk of
inducing
bronchoconstrictio
n
Limitations
if the test is performed
during a period of stable
or well-controlled
disease
Technical Factors
Safety
considerations
False-Positive
Results
Factors such as respiratory
infections, exposure to certain
irritants, or heightened anxiety
during the test
Limited
Applications
COPD or other non-asthmatic
causes of respiratory
symptoms

11. Thank you