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

Abstract

Background: Fraction of exhaled nitric oxide with an expiratory flow of 50 mL/s (F_ENO₅₀) 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_ENO₅₀ in liver transplant recipients and compare it to controls from the general population.

Methods: F_ENO₅₀ 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_ENO₅₀ 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_ENO₅₀ 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_ENO₅₀ (for F_ENO₅₀ ≥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_ENO₅₀ ≥25 ppb was 3.58 (95% CI: 2.50-5.15, p < 0.0001) and the adjusted OR for F_ENO₅₀ ≥50 ppb was 3.14 (95% CI: 1.37-7.20, p = 0.007)].

Conclusion: The liver transplant recipients had elevated F_ENO₅₀, implying increased eosinophilic airway inflammation. The clinical impact of this finding needs further investigation.

Keywords: comorbidity; eosinophilic airway inflammation; fraction of exhaled nitric oxide; liver transplant recipient; pulmonary disease.