Fractional Exhaled Nitric Oxide Cut-off Values for Discriminating Asthma Exacerbation and Control in Indian Children...

To determine Fraction of exhaled nitric oxide (FeNO) cut-off values that discriminate asthma exacerbation from control in Indian children with asthma and coexisting allergic rhinitis. Also, to evaluate the correlation between FeNO and Absolute eosinophil count (AEC).

A prospective observational cohort study with repeated measurements was conducted at a tertiary-care hospital in western India (March 2023-December 2024). Children aged 4-12 y with both conditions were consecutively enrolled. FeNO and AEC were measured at baseline, 1 mo and 3 mo. Asthma and allergic rhinitis case definition followed Global Initiative for Asthma (GINA) 2023 and Allergic Rhinitis and its Impact on Asthma (ARIA) 2016 guidelines. Optimal cut-offs were derived by ROC analysis with the Youden index.

Ninety-seven children (mean age 7.3 ± 2.2 y; 62.4% males) completed follow-up. FeNO and AEC correlated significantly during exacerbation (r = 0.361, p = 0.003) and control (r = 0.292, p = 0.036). A FeNO >20.5 ppb discriminated exacerbation with 77% sensitivity, 81% specificity, NPV 92.6%, PPV 52.6% (AUC 0.867, 95% CI 0.815-0.920; p <0.0001); the corresponding AEC was 505 cells/µL (AUC 0.828, 95% CI 0.769-0.887). For control, FeNO <14.5 ppb showed 55% sensitivity, 87% specificity, NPV 71% (AUC 0.739, 95% CI 0.675-0.803); corresponding AEC was 413 cells/µL.

FeNO and AEC are useful, complementary biomarkers in Indian children with asthma and coexisting allergic rhinitis. The proposed thresholds (FeNO >20.5 ppb for exacerbation, <14.5 ppb for control) are substantially lower than American Thoracic Society (ATS)/ European Respiratory Society (ERS) recommendations, supporting population-specific paediatric reference values.