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Introduction Recently data has demonstrated an association between blood eosinophil counts (BEC) and fractional exhaled nitric oxide (FeNO) levels and exacerbation risk, reinforcing the central role of T2 inflammation in asthma pathogenesis. Two point-of-care tests, airway oscillometry and spirometry, have been shown to synergistically increase the risk of poorer asthma control. Oscillometry can assess small airway resistance by the resistance heterogeneity between 5Hz and 20Hz (Rrs5–20).Methods The Oscillometry Asthma Registry (OAR) included adults diagnosed with asthma according to GINA. Data were retrospectively collected from two clinical sites: Ninewells Teaching Hospital in Dundee, UK, and the Allergy and Pneumology Outpatient Clinic in Bergamo, Italy. Four representative phenotypic groups were compared: (a) Group 1 – normal phenotype where Rrs5–20<0.10 kPa/L/s, FEV 1≥80%, BEC<300 cells/µL and FeNO<25ppb; (b) Group 2 – T2 high only phenotype where Rrs5–20<0.10 kPa/L/s, FEV1≥80%, BEC≥300 cells/µL and FeNO≥25ppb; (c) Group 3 – abnormal physiology only phenotype where Rrs5–20≥0.10 kPa/L/s, FEV1<80%, BEC<300 cells/µL and FeNO<25ppb; and (d) Group 4 – abnormal immuno-physiological phenotype where Rrs5–20≥0.10 kPa/L/s, FEV1<80%, BEC≥300 cells/µL and FeNO≥25ppb (figure 1a).Results 937 patients with mild to severe asthma were included. The adjusted odds ratio (aOR) [95% CI] for experiencing ≥1 and ≥2 exacerbations in Group 3 compared to Group 1 (reference group) was 3.77 (1.62,8.79) p<0.01, and 4.48 (1.35,14.85) p<0.05, respectively ( figure 1b). For Group 4 (abnormal physiology, T2-high), the aORs were substantially higher: 10.89 (4.89,24.25) p<0.001 for ≥1 exacerbation, and 12.39 (3.70,41.43) p<0.001 for ≥2 exacerbations, relative to Group 1 (figure 1b). This analysis was repeated using Group 4 as the reference group (figure 1c).Abstract S131 Figure 1Conclusion Future research should aim to prospectively incorporate small airways dysfunction alongside symptom burden, type 2 biomarkers and spirometry into a comprehensive longitudinal tool for predicting asthma exacerbation risk.