Exhaled nitric oxide stability over two years in relation to COPD outcomes.

The non-invasive biological marker exhaled nitric oxide (FENO) is increasingly used in asthma, but its clinical role in COPD is less established. FENOhas been reported to be both high and low outside the COPD exacerbation period. The study aimed to follow FENOvalues over two years during stable conditions in a cohort of COPD subjects participating in the TIE-study (Tools Identifying Exacerbation). The follow-up study included 353 subjects who attended three visits one year apart. The subjects that were ex-smokers (n= 265) had higher FENO,50values (median and IQR) compared with current smokers (n= 88), at inclusion 15 (10, 24) versus 9 (7, 15) ppb, after one year 15 (10, 24) versus 10 (7, 18) ppb, and after two years 14 (9, 22) versus 10 (7, 17) ppb, allp< 0.001. All subjects were further divided into two FENOgroups: <20 ppb (72%) and ⩾20 ppb (28%). After one year, 81% of the participants remained in the low group and 65% in the high FENOgroup. After two years, 71% remained in the low group and 52% in the high FENOgroup. The persistent low FENOgroup had statistically significantly lower FEV1%pred and FVC%pred compared to the high FENOgroup for all three visits. Among the ex-smokers, the proportion of subjects reporting dyspnoea (mMRC ⩾ 2) was higher in the persistent low FENOgroup than in the persistent high FENOgroup at all three visits. In conclusion, good consistency in FENOover two years is promising for monitoring FENOduring stable disease. COPD subjects with persistent low FENOhad poorer lung function and reported more dyspnoea than subjects with persistent high FENO.