The spirometric blind spot: oscillometry identifies a tobacco-dose-associated small-airway signal in community case-finding

Small-airway dysfunction (SAD) may precede fixed airflow obstruction, but the clinical meaning of increased oscillometric detection in community settings remains uncertain. In this cross-sectional study, we evaluated an oscillometry-defined SAD phenotype, its concordance with spirometric indices, and its association with cumulative tobacco exposure within an open-access community respiratory case-finding programme. Adults attending nine healthcare sites in Greece underwent structured questionnaire assessment, respiratory oscillometry and spirometry. Oscillometric SAD was defined as any abnormal R5–R19, X5, AX or Fres z-score, whereas spirometric SAD was defined as FEF₂₅–₇₅ <65% predicted. Complete acceptable oscillometric classification was available in 533/615 participants and complete acceptable spirometry in 504/615. Oscillometric SAD was present in 145/533 (27.2%), spirometric SAD in 71/504 (14.1%), and fixed-ratio airflow obstruction in 18/504 (3.6%). Among 468 participants with complete paired oscillometric and spirometric classifications, positive agreement was low (22.8%; Cohen’s κ = 0.055). Each additional 10 pack-years increased the adjusted odds of oscillometric SAD by 19% among ever-smokers (aOR 1.19, 95% CI 1.05–1.36; p = 0.007) and by 18% among ever-smokers with FEV₁/FVC ≥ 0.70 (aOR 1.18, 95% CI 1.03–1.36; p = 0.020). SAD was also observed in 15/56 participants with asthma (26.8%) and 57/191 never-smokers without a prior chronic respiratory diagnosis (29.8%). Oscillometry therefore identified a tobacco-dose-associated mechanical phenotype that was incompletely captured by spirometric criteria, but its substantial prevalence outside COPD limits disease-specific interpretation.