Dear Brigitte,
Thank you for raising this. We follow an approach most consistent with option 2, but we don’t apply a strict numerical cutoff when deciding whether to proceed with a mannitol challenge. If a patient’s baseline FEV₁ is <1.5 L or <70% predicted, we review the case individually rather than treating it as an automatic contraindication.
We take into consideration the patient’s age, duration and stability of their asthma, previous lung function, and current medication use. This helps us determine whether a low FEV₁ represents true ventilatory impairment or simply reflects normal physiology in a smaller adult. It also helps us to determine how well the patient is likely to recover with Ventolin if they experience a fall in FEV₁ during the challenge.
Aside from the safety concerns, there is the potential for interpretation uncertainty in patients with reduced baseline airway calibre. A low starting FEV₁ increases the likelihood of an exaggerated or false‑positive response, and for that reason, we will not proceed if we feel the baseline FEV₁ is too low to allow a reliable or safe test outcome.
Best wishes, Kate