Abnormal FeNO post COVID-19

ABSTRACT

Background: Airway inflammation post COVID-19 is a possible cause for persistent breathlessness. Aim(s) We sought to evaluate the role of fractional exhaled nitric oxide (FeNO) measurements in this cohort. Methodology: We report FeNO results in patients undergoing lung function testing as part of the PHENOTYPE study (NCT 04459351). Result(s) 83 patients had FeNO performed between January and Nov 2021. Of the patients admitted to hospital (n=78), the median time to testing from discharge was 96 days (IQR 90-115). Median FeNO results for the whole cohort was 20 ppb (16-29). 24/83 (29%) had a FeNO in the intermediate range [median 33 (IQR 28-45)], and 5/83 (6%), FeNO >50 ppb. Chi squared testing revealed no relationship between patient-reported breathlessness (p=0.12) or cough (p=0.45) and FeNO >=25ppb. 52 patients underwent repeat lung function and FeNO testing at a median of 363 (355-370) days post discharge. 26/52 (50%) of individuals had a FeNO>=25 ppb, with a median 35 (28-42) 10/52 (19%) deteriorated from normal to intermediate range and 2/52 from intermediate to high range as compared to initial values. 7/52 (13%) of FeNO results that were abnormal at the first visit, normalized with no additional treatment. Again, no association was found between breathlessness (p=0.48) or cough (p=0.73) at the second visit and a FeNO result >=25ppb. None of the patients with a FeNO >= 25 had a prior diagnosis of asthma. Conclusion(s) The clinical relevance of an intermediate or high FeNO in this cohort is unclear. However, this preliminary work highlights that in a significant proportion of patients, the FeNO is not normal even at 1 year post discharge. The trajectory of these changes and in particular, development of small airways disease are important to study.