OBJECTIVE: Ongoing airway inflammation measured by fractional exhaled nitric oxide (FENO) and airway hyperresponsiveness (AHR) to mannitol are associated in selected asthma patients, but no evidence exists of this association in unselected asthma patients. The aim was to investigate the association between FENO and AHR to mannitol in unselected individuals with possible asthma.

METHODS: A real-life study on patients with possible asthma referred to a specialized asthma clinic. Data on asthma history, FEV(1), FENO, atopy, smoking, treatment and AHR to mannitol were collected.

RESULTS: In 217 unselected patients with symptoms suggestive of asthma, FENO and response to mannitol were tested. Of the 141 who underwent both tests, 32 (23%) had FENO > 25 ppb, and 58 (41%) had AHR to mannitol. A significant association between high FENO and AHR was found (p < 0.001); 26% responded to mannitol despite a normal NO, and 8% had a high FENO but no AHR. Additionally, a weak association was found between log FENO and log response to mannitol (r = 0.32, p < 0.01). The area under the ROC curve for FENO as a predictor of AHR was 0.66 (95% CI 0.6-0.8) and for mannitol for having high FENO was 0.73 (95%CI 0.6-0.9).

CONCLUSION: In a large sample of patients referred to an asthma clinic, an association was found between FENO and AHR to mannitol. However, a significant proportion of asthma patients had a normal FENO despite having AHR, suggesting that in some patients, AHR to mannitol is not driven by eosinophilic airway inflammation.