DOI: 10.4103/sjim.sjim_47_25 ISSN: 1658-5763

Association between fractional exhaled nitric oxide and peripheral eosinophils in patients with asthma

Yahya Habis, Abdullah Sakkat, Reema Dafer, Shahad Hasan, Nada Hussain, Joud Mohammed, Atheer Alharbi
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ABSTRACT

Objective:

The primary endpoint was the correlation between fractional exhaled nitric oxide (FeNO) levels and peripheral eosinophil counts. Secondary endpoints included the associations of both biomarkers with bronchodilator responsiveness (BDR), Asthma Control Test (ACT) scores, spirometric parameters, and type 2 inflammatory comorbidities.

Patients and Methods:

This study included 101 patients with asthma. ACT scores, spirometry results, and BDR were assessed. Peripheral eosinophil count and percentage were recorded, and FeNO levels were measured and graded.

Results:

The mean age was 46.6 ± 14.6 years; 70 patients were female and 31 were male. The mean FeNO level was 68.9 ± 61.3 ppb, and the mean eosinophil count was 310.5 ± 344.2 cells/μL. FeNO levels were higher, though not statistically significantly among current and former smokers than among nonsmokers ( P = 0.85) and among patients with allergic rhinitis ( P = 0.13), chronic rhinosinusitis/nasal polyposis ( P = 0.36), and eczema/atopic dermatitis ( P = 0.62). The mean FeNO levels were comparable across airway obstruction grades ( P = 0.81) but were higher, without reaching statistical significance, in patients with controlled ACT scores ( n = 38, 77.8 ± 74.7 ppb; P = 0.47). FeNO levels were significantly higher in patients with eosinophil counts ≥ 300 cells/μL ( n = 30, 96.2 ± 82.1 ppb; P = 0.012). FeNO showed a positive but nonsignificant correlation with eosinophil count ( r = 0.16, P = 0.11) and a significant correlation with BDR ( r = 0.38, P = 0.001). Eosinophil counts did not significantly correlate with BDR ( r = 0.008, P = 0.095). FeNO showed modest, nonsignificant discriminatory ability between patients with and without allergic rhinitis ( P = 0.059). Both eosinophil count and FeNO demonstrated similar performance in differentiating chronic rhinosinusitis with nasal polyposis ( P = 0.17 and P = 0.15), gastroesophageal reflux disease ( P = 0.87 and P = 0.85), and eczema/atopic dermatitis ( P = 0.11 and P = 0.24), respectively.

Conclusion:

FeNO levels were significantly associated with peripheral eosinophil counts (≥300 cells/μL), supporting its role as a biomarker of type 2 (T2) airway inflammation. As a secondary finding, FeNO was also significantly associated with BDR. Elevated FeNO may indicate active eosinophilic airway inflammation, increased peripheral eosinophil counts, and better-controlled asthma.

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