Value of the FEF50/0.5FVC Ratio in the Identification of Obstructive Ventilatory Defects in Asthmatic Children

<b><i>Introduction:</i></b> Pediatric asthma is a common condition that requires early detection of obstructive ventilatory defects (OVDs) for optimal management. While the forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) ratio is widely used in spirometry, it may lack sensitivity in children, especially in detecting mild or early obstruction. This study aimed to assess the utility of the forced expiratory flow (FEF) at 50% of FVC to the half of FVC (FEF50/0.5FVC) ratio as a complementary tool for identifying OVD in asthmatic children. <b><i>Methods:</i></b> This was a retrospective study conducted on 165 asthmatic children (aged 5-15 years). Spirometric data including FEV1, FVC, FEV1/FVC, FEF50, FEF at 25%-75% of FVC (FEF25%-75%), and peak expiratory flow were analyzed. The FEF50/0.5FVC ratio was calculated for each child. OVD was defined as an FEV1/FVC ratio below the lower limit of normal, based on Z-scores. Statistical analysis included <i>t</i>-tests, Pearson's correlation, and receiver operating characteristic (ROC) curve analysis to compare the diagnostic efficiency of the FEF50/0.5FVC ratio with traditional spirometric measures. <b><i>Results:</i></b> OVD was identified in 25.5% of participants. The FEF50/0.5FVC ratio was significantly lower in the OVD group (1.23 ± 0.24) compared with the normal spirometry group (2.08 ± 0.5, <i>P</i> < 0.0001). A strong correlation was observed between the FEV1/FVC ratio and FEF50/0.5FVC (r = 0.88, <i>P</i> < 0.001). ROC analysis showed that the FEF50/0.5FVC ratio had superior diagnostic accuracy for OVD (area under the curve = 0.948, 95% confidence interval 0.899-0.996) compared with other spirometric indices, with a sensitivity of 91% and specificity of 90.2% at an optimal threshold of 1.56. <b><i>Conclusion:</i></b> FEF50/0.5FVC ratio is a promising tool for detecting OVD in asthmatic children, demonstrating high sensitivity and specificity. It may outperform traditional spirometric measures in identifying subtle airway obstructions, offering a valuable addition to routine asthma diagnostics, particularly in pediatric patients with early-stage or mild asthma.