FEV1 and eNO reflects clinical characteristics rather than asthma control in children with asthma

<bold>Introduction:</bold> Forced expiratory volume in one second (FEV1) and exhaled nitric oxide (eNO) are commonly used to assess asthma control, but their correlation remains unclear. <bold>Objective:</bold> This study hypothesized that FEV1 and eNO reflect clinical characteristics rather than asthma control and investigated their changes across clusters classified by baseline values. <bold>Methods:</bold> This study included 626 children aged 5–15 years with asthma from the Korean Childhood Asthma Study (KAS) cohort, classifying them into four clusters based on baseline FEV1 and eNO using hierarchical analysis. Longitudinal analysis over 12 months at 6-month intervals and correlation tests assessed associations with asthma control. <bold>Results:</bold> Four clusters were identified based on FEV1 and eNO levels [Cluster 1: FEV1 94.96 ± 8.33%, eNO 57.05 (37.21–87.48) ppb; Cluster 2: FEV1 92.36 ± 7.31%, eNO 11.90 (7.95–17.83) ppb; Cluster 3: FEV1 76.83 ± 12.50%, eNO 28.62 (17.61–46.51) ppb; Cluster 4: FEV1 109.53 ± 6.64%, eNO 20.98 (12.26–35.90) ppb]. Cluster 3 showed the most significant increase in FEV1, while Cluster 1 exhibited the largest decrease in eNO [FEV1 change in Cluster 3: 13.94% ± 25.11%; eNO change in Cluster 1: -38.68% (-71.9–46.85%)]. Despite these variations, cluster characteristics remained stable over 12 months. Furthermore, neither FEV1 nor eNO reflected asthma control at any time point or predicted future control. <bold>Conclusion:</bold> Asthma clusters based on FEV1 and eNO remained stable over 12 months, and neither parameter correlated with asthma control. These findings suggest that FEV1 and eNO primarily reflect clinical characteristics rather than asthma control.