Bronchial provocation tests: the rationale for using inhaled mannitol as a test for airway hyperresponsiveness.

The use of histamine and methacholine is well established for identifying airway hyperresponsiveness (AHR) but the AHR to these agents is not specific for asthma diagnosis. Further, these agents do not identify or exclude exercise-induced asthma (EIA) so they are inappropriate for some occupational and sporting assessments. Measurement of AHR by pharmacological agents has other limitations in that a positive response does not necessarily identify a person who will respond to inhaled steroids and responses do not differentiate between doses of steroids. As most asthmatics remain hyperresponsive to these agents after treatment they have not been useful for guiding steroid dose reduction. Bronchial provocation tests (BPTs) with physical stimuli such as exercise, eucapnic voluntary hyperpnea and hypertonic saline have provided useful information on presence and severity of asthma and EIA. These tests however, can be time consuming and require more resources compared with the pharmacological tests. To simplify testing, a challenge has been developed that uses a dry powder of mannitol administered from a simple hand-held device. The mannitol is given in increasing doses from capsules containing from 5 mg to 40 mg. Mannitol responsiveness identifies people with EIA and those who will respond to inhaled steroids. Mannitol responsiveness is reduced following treatment with inhaled steroids, and some subjects become unresponsive within 6 to 8 weeks. Responsiveness to mannitol can be used to predict risk of exacerbation during back titration of steroids. Should this BPT become more readily available it would be the first to provide a common operating standard for use in the laboratory, office, or field.