From the Guidelines
The airway hyperresponsiveness in a patient with a 15% decrease in FEV1 at a cumulative dose of 30mg mannitol should be defined as moderate to severe, indicating significant bronchial hyperreactivity and potential for active airway inflammation, as supported by the most recent and highest quality study 1. This result indicates that the patient reached the threshold for a positive test at a relatively low dose of mannitol, suggesting that the airways are highly sensitive to the osmotic stimulus.
Key Points to Consider
- The mannitol challenge test typically involves administering increasing doses with a positive test defined as either a 15% fall in FEV1 at any dose or a 10% fall between consecutive doses.
- A 15% decrease in FEV1 at a cumulative dose of 30mg mannitol is a significant response, indicating moderate to severe airway hyperresponsiveness.
- This level of hyperresponsiveness correlates with more symptomatic asthma and potentially greater risk of exacerbations, as noted in studies such as 1 and 1.
Clinical Implications
- Clinically, this indicates the patient likely has active airway inflammation and may require more aggressive anti-inflammatory treatment, such as inhaled corticosteroids.
- The test works because mannitol creates an osmotic gradient that triggers mast cell degranulation and mediator release in susceptible airways, mimicking the mechanism of exercise-induced bronchoconstriction, as described in 1.
Relevant Guidelines and Studies
- The British guideline on the management of asthma 1 and the American Thoracic Society/European Respiratory Society statement 1 provide guidance on the diagnosis and management of asthma, including the use of mannitol challenge tests to assess airway hyperresponsiveness.
- Studies such as 1 have demonstrated the effectiveness of mannitol challenge tests in identifying patients with asthma and monitoring their response to treatment.
From the Research
Definition of Airway Hyperresponsiveness
Airway hyperresponsiveness can be defined as a 15% change in Forced Expiratory Volume in 1 second (FEV1) at a certain dose of mannitol during a mannitol challenge test.
- The dose of mannitol required to cause a 15% fall in FEV1 is often referred to as the provoking dose of mannitol (PD15) 2, 3, 4.
- A study published in 2005 found that a 15% fall in FEV1 defined a positive test for airway hyperresponsiveness 2.
- Another study published in 2022 also used a 15% fall in FEV1 as the criteria for a positive test 3.
Mannitol Challenge Test
The mannitol challenge test is a bronchial provocation test used to assess airway hyperresponsiveness.
- The test involves inhaling increasing doses of mannitol until a 15% fall in FEV1 is achieved or a maximum cumulative dose is reached 2, 4, 5.
- The test is simple, inexpensive, and can be performed in an office setting 4, 6.
- Common adverse events associated with the test include cough, headache, and pharyngolaryngeal pain 2, 6.
Diagnostic Criteria
The diagnostic criteria for airway hyperresponsiveness using the mannitol challenge test are based on the dose of mannitol required to cause a 15% fall in FEV1.
- A study published in 1998 found that 69% of subjects had a positive response to mannitol after less than 155 mg (6 capsules) and 94% less than 320 mg (10 capsules) 4.
- Another study published in 2003 found that the geometric mean provoking dose of mannitol causing a 10% fall in FEV1 was 202 mg 5.
- The sensitivity and specificity of the mannitol challenge test in diagnosing airway hyperresponsiveness have been reported to be high, with sensitivity ranging from 80.7% to 96% and specificity ranging from 86.7% to 92% 2, 3, 5.