Small airway dysfunction in asthma: concordance and discordance between spirometry and oscillometry in real-life

Background. Small airway dysfunction (SAD) is increasingly recognized as a key feature in asthma, influencing control, exacerbations, and severity. Spirometry remains the gold standard for lung function assessment but mainly reflects large airways, whereas impulse oscillometry (IOS) offers complementary insights into peripheral airway function. Methods. A retrospective analysis was conducted on 218 patients referred for asthma-like symptoms or untreated mild asthma to the Allergy and Clinical Immunology Unit of L. Sacco Hospital (Milan). All underwent spirometry and IOS; 169 also completed bronchodilator testing. Concordance, discordance, and correlations were evaluated using chi-square tests, logistic regression, and Pearson's coefficient. Results. Among 218 patients (mean age 40 years, 62% female), SAD was detected in 24 by spirometry and 52 by IOS, with significant overall concordance (p < 0.001), particularly in patients with asthma-like symptoms. Discordance was associated with older age, female sex, and higher body mass index. Bronchodilator testing showed discordant responses, correlating with exertional symptoms and lower Asthma Control Test (ACT) scores. Conclusions. IOS and spirometry provide complementary insights into airway physiology. IOS is more sensitive to peripheral airway abnormalities and can detect distinct bronchodilator responses, whereas spirometry remains the standard assessment tool. Their combined use improves detection and monitoring of small airway dysfunction, especially in early or mild asthma, potentially guiding more personalized management strategies.