Clinical Utility of Central and Peripheral Airway Nitric Oxide in Children with Different Types of Allergic Asthma.

Background: Fractional exhaled nitric oxide has been widely used as a biomarker of airway inflammation. By measuring nitric oxide concentrations at different exhalation flow rates, it is possible to assess inflammation in various segments of the respiratory tract. This study hypothesized that FeNO could serve as a valuable tool for evaluating airway inflammation in children with different types of allergic asthma. Methods: This retrospective single-center study included 487 children with asthma, categorized as inhalant-sensitized (n=238), food-sensitized (n=36), mixed-sensitized (n=181), and non-sensitized controls (n=32). Fractional exhaled nitric oxide was measured following ERS/ATS protocols, including FeNO50 (flow rate 50 mL/s), FeNO200 (200 mL/s), and CaNO (alveolar or peripheral airway NO concentration). Multivariable median regression was used to assess group differences after adjusting for age, sex, BMI, inhaled corticosteroid (ICS) use, rhinitis, and recent respiratory infection. Results: FeNO50 and FeNO200 levels were significantly higher in both the inhalation allergen and mixed allergen groups compared to the control and food allergen groups (all adjusted P < 0.01). For instance, FeNO50 showed an adjusted median difference of -5.00 ppb (95% CI: -8.50, -2.00; P =0.003) between the control group and inhalations. CaNO levels did not differ significantly across groups (P = 0.133). Conclusion: FeNO50 and FeNO200 levels were significantly higher in inhalant- and mixed-sensitized children compared with food-sensitized or non-sensitized controls, indicating stronger type-2 inflammatory features. CaNO showed no significant difference across groups after adjustment. These findings highlight FeNO as a potential biomarker associated with airway inflammation in sensitized asthma; however, further prospective studies are warranted for confirmation.