Stability of FeNO and airway hyperresponsiveness to mannitol in untreated asthmatics

Airway hyperresponsiveness and airway inflammation are important hallmarks of asthma and are useful in asthma diagnosing, monitoring and treatment. The aim of the study was to assess whether two commonly used clinical tests, the mannitol challenge and Fraction of exhaled NO (FeNO), were stable clinical indicators over time in stable untreated asthmatics.

54 non-smoking, asthma patients not treated with steroids were enrolled in the study and assessed at baseline and a median of 6 months later. At baseline and follow-up, FeNO and airway hyperesponsiveness to mannitol were measured, and asthma control was assessed with the Asthma Control Questionnaire (ACQ).

A total of 41 subjects completed both visits. Mean (SD) FEV1% at baseline was 94.1% (17.7) and at re-examination 94.6% (19.7) (ns). The ACQ score was unchanged from baseline (Mean (SD): 0.90 (± 0.73)) to follow-up 0.90 (± 0.74) (ns), as was the FEV₁% (94.1% (±17.1%) vs 94.6% (19.7%)(ns) indicating that patients were clinically stable during follow-up. The response to mannitol was unchanged at follow-up (Geometric mean (CI) of Response Dose Ratio (RDR) to mannitol: 0.026(0.013-0.046) vs 0.026(0.012-0.050) (ns). There was a slight decrease in FeNO at follow-up (25.5 ppb (19.7-32.9) to 21.9 ppb (17.1-28.2) (p < 0.001).

In steroid-free non-smoking asthmatics with constant symptom scores and lung function, airway responsiveness to mannitol remained at the same level over a period of months, while a minor change in exhaled FeNO was reported. These results suggest that mannitol is a stable, reliable marker of clinical disease activity.