What is the definition of airway responsiveness as determined by a mannitol (inhalation challenge test)?

From the Guidelines

Airway responsiveness in the mannitol challenge test is defined by a fall of ⩾15% in FEV1 from baseline in response to the cumulative total dose or a 10% decrease between two consecutive doses of mannitol. This definition is based on the European Respiratory Society clinical practice guidelines for the diagnosis of asthma in children aged 5-16 years, as outlined in a 2021 study published in the European Respiratory Journal 1. The mannitol challenge test is a diagnostic tool used to assess airway responsiveness, which involves inhaling increasing doses of mannitol, an osmotic agent, via a dry-powder inhaler device, with FEV1 measured repeatedly between the inhalation steps. Some key points to consider when interpreting the results of the mannitol challenge test include:

• The test is considered positive if there is a fall of ⩾15% in FEV1 from baseline in response to the cumulative total dose or a 10% decrease between two consecutive doses of mannitol 1
• The test should be performed with caution in certain patient populations, such as those with severe airflow limitation or recent respiratory infections
• Bronchodilators should be withheld before testing to ensure accurate results
• The mannitol challenge test is particularly useful for diagnosing exercise-induced bronchoconstriction, as it mimics the airway-drying effect of exercise. Overall, the mannitol challenge test is a valuable diagnostic tool for assessing airway responsiveness and diagnosing conditions such as asthma and exercise-induced bronchoconstriction, and its results should be interpreted in the context of the patient's clinical presentation and medical history.

From the Research

Definition of Airway Responsiveness

The definition of airway responsiveness as determined by a mannitol inhalation challenge test can be understood through various studies.

• Airway hyperresponsiveness is a characteristic feature of asthma, and its measurement using indirect challenges, such as mannitol, is important in establishing a correct diagnosis 2.
• The mannitol challenge test is defined by a PD15 of <635 mg, which indicates airway responsiveness 3, 4.
• A positive mannitol test is defined as a 15% decline in FEV1 (PD15) at a dose of <635 mg of mannitol 3.

Determinants of Airway Responsiveness

Several factors can influence the results of a mannitol challenge test, including:

• Female gender, increasing BMI, exercise-induced cough, night-time respiratory symptoms, low FEV1/FVC ratio, and high FENO are determinants for a positive mannitol test 3.
• The sensitivity and specificity of the mannitol challenge test can vary, with reported values of 48.0% and 92.6%, respectively 4, and 56% and 94%, respectively 3.

Comparison with Other Challenge Tests

The mannitol challenge test can be compared to other bronchial provocation tests, such as the methacholine challenge test.

• The diagnostic properties of the methacholine and mannitol bronchial challenge tests have been compared, with similar diagnostic properties but intercomplementary roles for asthma diagnosis 4.
• Indirect challenge tests, such as the mannitol test, correlate better with eosinophilic airway inflammation and are seen as more specific than direct challenge tests 2.