Measurement of exhaled nitric oxide (FENO50) has been proposed in COPD patients seeking medical attention for suspected exacerbation1. However, FENO50 has been shown to be both high and low outside the exacerbation period.
We studied the consistency of FENO50 over 2 years in ex-smokers from a cohort of COPD subjects with spirometry-verified diagnosis (TIE-study). The following groups were defined for inclusion, 1- and 2-year follow-up: consistently FENO50 ?20 ppb (group A, n=119), consistently FENO50 >20 ppb (group B, n=46) or with variable FENO50 (group C, n=100).
The FENO50 at the inclusion visit (median, IQR) was for group A 11 (8,13), B 33 (27, 51) and C 18 (14, 24) ppb. No difference was found between the groups regarding age, sex, BMI, asthma, chronic bronchitis, COPD Assessment Test, or having received a COPD diagnosis before the age of 50. No differences were found regarding ICS treatment or frequency of exacerbation over the 2 years. The proportion of patients with hospital visits due to exacerbations was in A, B and C, 14%, 4 % and 8%, respectively (p=0.11). Dyspnoea, defined as mMRC?2, was reported more frequently at all visits by group A (all p-values <0.05). Group A had higher B-neutrophils, lower B-eosinophils and lower FEV1 than group B at all three visits (all p-values <0.05). It took longer time to walk 30 m at maximal pace in group A than in B at all three visits (all p-values <0.05). After two years, the Clinical COPD Questionnaire was higher in group A compared to B (p<0.01).
In conclusion, COPD subjects with consistently low FENO50 had characteristics of more severe disease than subjects with consistently high FENO50, despite no difference in the reported co-morbidities.
1Stolz et al.Lancet 2022