Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 24 3 2025 05 05 277 282 Maryam Heydarazad zadeh Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Seyed Alireza Mahdaviani Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Alireza Eslaminejad Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran Mahsa Rekabi Pediatric Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran 2024 09 04 2025 01 11 Measuring the performance of small airways dysfunction is challenging due to their relative inaccessibility with conventional methods. In recent years, spirometry and impulse oscillometry (IOS) methods have been widely used for their evaluation. The aim of this study was to investigate the relationship between spirometric parameters and IOS in newly diagnosed asthma (NDA) patients. In this cross-sectional study, 100 NDA patients who referred to the allergy Clinic of Masih Daneshvari Hospital between 2021 and 2023 were enrolled. IOS and spirometry tests were performed for all patients. Spirometry measures included forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), FEV1/FVC, and forced expiratory flow (FEF25-75). IOS criteria included R5%, R20%, R5-R20%, X5%, Ax% and FRES. The relationship between spirometry and IOS parameters was evaluated. The mean age was 22.6±9.5 years. None of the 2 techniques had a significant relationship with disease severity. FVC, FEV1/FVC and FEF25-75 indices had a significant positive correlation with all other IOS indices except for Ax. In the comparison of FEF25-75 parameter in spirometry, 4 IOS indices including R5, R20, R5-R20 and X5 had appropriate sensitivity and specificity for predicting asthma. In the comparison of FEF25-75 parameter in spirometry, 4 IOS indices including R5, R20, R5-R20 and X5 had appropriate sensitivity and specificity for predicting asthma. The sensitivity and specificity of R5 for asthma diagnosis were 0.85 and 0.73, respectively. Further multicenter studies with larger sample sizes are recommended to confirm these results. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/4192 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/4192/2180