Optimal cut-offs for SAD indicators in predicting airflow obstruction

<bold>Background:</bold> Small airways dysfunction (SAD) contributes a major role in chronic obstructive pulmonary disease and suspected to be an early indicator for future disease development. We assess the ability of SAD markers on prediction of development of airflow obstruction (AO). <bold>Methods:</bold> Participants from Austrian general adult population (LEAD cohort) without any COPD or Asthma diagnosed and with normal lung function (FEV1/FVC≥LLN) in the baseline (n=5746) included in the study. We analysed the development of AO in average duration of 4 years. We compared the ability of SAD indicators, including forced mid-expiratory flow FEF25-75% and FEF25-75%/FVC, in the prediction of AO (FEV1/FVC<LLN) using Receiver Operating Characteristic (ROC) analysis. <bold>Results:</bold> 223 (3.9%) participants developed an airflow obstruction in the follow-up visit. ROC analysis showed that FEF25-75%/FVC z-score performs better with the maximum Area Under Curve (AUC=0.885 compared to 0.839, 0.872, and 0.725 for FEF25-75%/FVC, FEF25-75% z-score, and FEF25-75%, respectively) in predicting development of AO within 4 years until the next follow-up visit (Fig. 1). The optimal cut-off (−0.7814) is calculated using Youden index which maximizes the sum of sensitivity and specificity. <bold>Conclusions:</bold> This cut-off is a spirometric marker to identify risk for AO and can be applied for an early hint to participants with a normal lung function who have the risk to develop AO in 4 years. <fig><object-id>erj;64/suppl_68/PA3068/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>