Fractional Exhaled Nitric Oxide as a Biomarker for Patients Post COVID-19

Shot of a man coughing while recovering from an illness on the sofa at home
Do FeNO levels in those who have recovered from COVID-19 serve as a biomarker for post-COVID syndrome?

Fractional exhaled nitric oxide (FeNO) may not be a useful biomarker in post-COVID-19 patient monitoring, according to research findings published recently in Respiratory Medicine. Researchers also suggested that COVID-19 does not induce chronic bronchial inflammation or predispose individuals to chronic obstructive diseases.

Researchers sought to test the hypothesis that FeNO would be a useful biomarker in patients following COVID-19, given the nature of inflammatory and fibrotic processes found in these patients. Toward that end, the researchers conducted a prospective pilot study included 68 adult post-COVID-19 patients (mean 53.6 years of age, 25 of 68 female), who had been admitted less than 2 months after the onset of COVID-19 to 2 hospitals in Benevento and Salerno, Italy, to undergo a pulmonary rehabilitation program or to continue appropriate medical care. The study also included 29 healthy controls (mean age 47.2 years; 10 females).

All participants had their FeNO measured via electrochemical analyzer. The mean FeNO value for the COVID-19 cohort was 18.55 ppb (95% CI, 15.50-21.58) and the mean FeNO value for the control group was 17.46 ppb (95% CI, 15.75-19.17), resulting in a non-statistically significant difference (P =.053). Researchers also reported the mean FeNO of post-COVID-19 patients in males (20.97 ppb; 95% CI, 16.61-25.33) was higher than in females (14.36 ppb; 95% CI, 11.11-17.61) with a statistically significant difference (P =.016). The control group showed no significant difference between male and female (P =.534) (male: 17.05 ppb; 95% CI, 15.01-19.09; female: 18.24 ppb; 95% CI,14.61-21.87).

Researchers concluded that, “The data generated in this study suggest that measurement of FeNO is not useful as a biomarker of post-COVID-19 patient monitoring.” Researchers said that the similarity in FeNO mean values in post-COVID-19 patients and the control group, “suggests that COVID-19 does not induce chronic bronchial inflammation or predispose to chronic obstructive diseases.”

This study was limited by its small sample size, said researchers. They added that “Our data do not allow us to understand whether FeNO values are elevated in patients with COVID-19, with possible differences between those with versus without pneumonia or acute respiratory distress syndrome, and then decrease in the post-COVID phase.”


Maniscalco M, Ambrosino P, Poto R, et al. Can FeNO be a biomarker in the post-COVID-19 patients monitoring? Respiratory Medicine. Published online January 25, 2022. doi:10.1016/j.rmed.2022.106745