Objectives In this study we aimed to explore the efficacy of FeNO (The fraction of exhaled nitric oxide) measurement in determining airway inflammatory phenotype in chronic cough patients. FeNO is a biomarker of eosinophilic inflammation. Sequential patients attending a specialist cough clinic were classified as low FeNO (FeNO ≤20 ppb) or high FeNO (FeNO ≥30 ppb) to evaluate the profile of other eosinophilic biomarkers (blood and sputum), cough frequency, and demographics to determine if they exhibited phenotypic variability.

Methods In total 49 patients completed the baseline visit. Correlations between FeNO, blood and sputum eosinophil cell count were assessed. We then compared the objective and subjective measurements of cough in patients with high FeNO and low FeNO at baseline. 24 hour cough counts were measured using the Hull Automated Cough Counter (HACC). Hull Airways Reflux Questionnaire (HARQ) and Leicester Cough Questionnaire (LCQ) were applied to measure cough subjectively.

Results There was a marked gender difference between groups with the low FeNO group having 90% women whereas the sexes were equally represented in the high FeNO cohort. The predominantly female, low FeNO group had more than twice the number of coughs recorded. Again at baseline there was a significant difference in HARQ and LCQ scores between high and low FeNO groups. Patients with low FeNO suffered more from cough symptoms in comparison with patients with high FeNO according to the 24 hour cough count, HARQ and LCQ scores. FeNO value had a strong correlation with blood and sputum eosinophil count (r=0.79 and r=0.65 p<0.001 respectively).

Conclusions By evaluating the demographic data, 24 hours cough count, HARQ and LCQ in high FeNO and low FeNO groups, different characteristics between these two cohorts observed. FeNO predicted the gender-related differences in demographic, with women markedly over represented in the low FeNO cohort. A female preponderance in patients with chronic cough has been well documented. However, the possible relationship between different inflammatory profiles as reflected by FeNO has not previously been described.