How stopping inhaled corticosteroid puffers for different periods before a breathing test affects the accuracy of asthma diagnosis in adults.

Participants allocated to the intervention arm (Group B) will be required to withhold their usual inhaled corticosteroid (ICS) therapy for seven days prior to bronchoprovocation testing. Following completion of the seven-day withholding period, participants will undergo a standard bronchoprovocation test. If the initial bronchoprovocation test result is negative, participants will continue to withhold ICS therapy for a total duration of three weeks, after which the bronchoprovocation test will be repeated. Participants will be provided with written instructions detailing the ICS withholding requirements, an asthma action plan, and contact details for clinical support throughout the withholding period. On each test day, participants will undergo fractional exhaled nitric oxide (FeNO) testing, baseline spirometry, a bronchoprovocation challenge, and post-challenge spirometry, and will complete the Asthma Control Questionnaire (ACQ-5). The intervention will be delivered face to face and on an individual basis by respiratory scientists, with oversight of participant safety provided by a respiratory nurse practitioner. Participants may also receive telephone contact during the withholding period for clarification or support, as required. Participants who experience significant worsening of symptoms or require systemic corticosteroids during the withholding period will be withdrawn from the intervention and managed in accordance with their asthma action plan and standard clinical care. Adherence to the intervention will be assessed at the testing visit by confirmation of the timing of the participant’s last ICS dose. Fidelity will be supported through standardised written instructions, predefined testing protocols, investigator blinding to group allocation, and routine data quality and safety monitoring. No study medications will be administered.