Fraction of exhaled nitric oxide is higher in liver transplant recipients than in controls from the general population: a cohort study

Background: Fraction of exhaled nitric oxide with an expiratory flow of 50 mL/s (F _ENO ₅₀) is a biomarker of eosinophilic airway inflammation. Liver transplant recipients have an increased risk of pulmonary infections, but little is known about the burden of chronic pulmonary diseases in this group. We aimed to assess the prevalence of elevated F _ENO ₅₀ in liver transplant recipients and compare it to controls from the general population. Methods: F _ENO ₅₀ was measured in 271 liver transplant recipients from The Danish Comorbidity in Liver Transplant Recipients (DACOLT) study and 1,018 age- and sex-matched controls from The Copenhagen General Population Study (CGPS). Elevated F _ENO ₅₀ was defined as ≥25 or ≥50 parts per billion (ppb). The analyses were adjusted for known and suspected confounders. Results: The median age of the liver transplant recipients was 55 years (interquartile range (IQR) 46–64), and 58% were men. The liver transplant recipients had a higher median F _ENO ₅₀ than the controls [16 ppb (IQR 10–26) vs. 13 ppb (IQR 8–18.), p < 0.001]. Furthermore, the liver transplant recipients had a higher prevalence of elevated F _ENO ₅₀ (for F _ENO ₅₀ ≥25 ppb 27% vs. 11%, p < 0.001 and ≥50 ppb 4% vs. 2%, p = 0.02). The results were similar after adjusting for age, sex, smoking status, use of airway medication, and blood eosinophil counts [the adjusted odds ratio (OR) for F _ENO ₅₀ ≥25 ppb was 3.58 (95% CI: 2.50–5.15, p < 0.0001) and the adjusted OR for F _ENO ₅₀ ≥50 ppb was 3.14 (95% CI: 1.37–7.20, p = 0.007)]. Conclusion: The liver transplant recipients had elevated F _ENO ₅₀, implying increased eosinophilic airway inflammation. The clinical impact of this finding needs further investigation.