Grading the severity of airways obstruction by spirometry - comparison of ERS/ATS 2021 and 2005 technical standards

<bold>BACKGROUND:</bold> Assessing severity of airways obstruction is crucial for effective disease management. The evolving knowledge of lung physiology provides revised criteria for severity grading. Despite updated interpretative strategies in 2021 (ERS/ATS 2021), the older 2005 strategy (ERS/ATS 2005) is deemed simpler and used widely. We therefore assessed the concordance and discordance between the two. <bold>METHODS:</bold> A retrospective study was done in our Southern Indian tertiary care hospital. Outpatients with clinical diagnoses of obstructive airway diseases tested for the first time by spirometry from Sept–Dec, 2023 were included. Indian population-specific reference equations were used to compute the predicted values. Obstruction was diagnosed by FEV1/FVC<5th percentile and severity was graded by the ERS/ATS 2005 using FEV1%Pred values and by the ERS/ATS 2021 using z-scores for FEV1. <bold>RESULTS:</bold> 2126 patients (57.6% males; mean age 46.38 ± 15.04; 11.2% current smokers) were included in the study. 629(29.5%) had obstructive defect and on these, gradings were evaluated. Overall concordance was seen in 384(61.04%) patients; Weighted Kappa: 0.596; moderate agreement; (p<0.001). 1-grade difference was seen in 33.1%, 2-grade difference in 5.7%, and 3-grade difference in 0.2% of patients. The agreement appeared to decrease with increasing obstruction (No impairment-73.1%; Mild-59.2%; Moderate-65.8% and Severe-38.8%). The agreement was higher in males, non-smokers and asthmatics. <bold>CONCLUSION:</bold> Only moderate agreement was found between the two standards, with a 2-grade or more difference occurring in 5.9% of patients. Transition to new ERS/ATS 2021 technical standards seems imperative.