What is the methacholine (MCH) test for?

From the Guidelines

The methacholine challenge test is primarily used to diagnose asthma by assessing airway hyperresponsiveness, as it has a high negative predictive power, making it more useful in excluding a diagnosis of asthma than in establishing one 1.

Key Points

• The test involves inhaling increasing concentrations of methacholine, a substance that causes airway constriction in sensitive individuals, with lung function measured after each dose using spirometry 1.
• A significant drop in forced expiratory volume (typically 20% or more) indicates a positive test, suggesting asthma, and is particularly useful when asthma is suspected but standard pulmonary function tests are normal 1.
• Methacholine works by stimulating cholinergic receptors in airway smooth muscle, causing bronchoconstriction, and people with asthma have airways that are hypersensitive to this stimulus, responding at much lower doses than those without asthma 1.
• The test is contraindicated in patients with severely reduced lung function, recent heart attack, stroke, uncontrolled hypertension, or aortic aneurysm.

Clinical Use

• The methacholine challenge test is a valuable tool in the evaluation of occupational asthma and chronic cough due to asthma or non-asthmatic eosinophilic bronchitis (NAEB) 1.
• It is recommended to use the test in patients with suspected NAEB, and in patients with asthma whose cough is refractory to initial corticosteroid therapy 1.
• The test results should be interpreted in the context of the patient's clinical history and other diagnostic tests, such as spirometry and assessment of airway inflammation 1.

From the FDA Drug Label

Provocholine, used in a methacholine challenge test, is indicated for the diagnosis of bronchial airway hyperreactivity in adults and pediatric patients five years of age and older who do not have clinically apparent asthma.

The methacholine test is used for the diagnosis of bronchial airway hyperreactivity in adults and pediatric patients five years of age and older who do not have clinically apparent asthma 2, 2, 2.

• The test is indicated for patients without clinically apparent asthma.
• It is used to assess bronchial airway hyperreactivity.
• The test should only be performed by adequately trained personnel in a pulmonary function laboratory or clinic.

From the Research

Methacholine Test Overview

• The methacholine test is a diagnostic tool used to assess airway responsiveness and diagnose asthma 3, 4, 5, 6, 7.
• It involves inhaling increasing concentrations of methacholine, a substance that can trigger airway constriction, to measure the level of airway responsiveness 5.

Purpose of the Methacholine Test

• The primary purpose of the methacholine test is to diagnose asthma by detecting airway hyperresponsiveness, a hallmark of the disease 3, 4, 6, 7.
• It can also be used to assess the severity of asthma and monitor the effectiveness of treatment 4.
• Additionally, the test can be used to identify individuals with occupational asthma and to assess the effects of potential sensitizers or treatments 5, 6.

How the Methacholine Test Works

• The test measures the provocative concentration of methacholine required to cause a 20% fall in forced expiratory volume in one second (FEV1), known as PC20 3, 4, 5, 7.
• A lower PC20 value indicates greater airway responsiveness and is often associated with asthma 3, 4, 5.
• The test can be used in conjunction with other diagnostic tools, such as peak expiratory flow monitoring and bronchodilation tests, to confirm an asthma diagnosis 3, 7.

Clinical Significance of the Methacholine Test

• The methacholine test has been shown to be a valuable diagnostic tool in clinical practice, with a sensitivity of around 60% and a specificity of around 90% for diagnosing asthma 5.
• The test can also provide information on the severity of asthma and the effectiveness of treatment, making it a useful tool for clinicians 4, 6.
• However, the test is not without limitations, and its results should be interpreted in conjunction with other diagnostic tools and clinical findings 5, 7.