Introduction: in 2005 Pellegrino et al¹ published interpretation strategies for spirometry. In 2021 an update was published by Stanojevic² et al. In this retro prospective study  the focus will be on the degree of severity in obstruction. Pellegrino et al used %predicted in the classification while Stanojevic used Z- scores.
Methods: a retro prospective study in a general hospital with 750 patients, who performed spirometry (pre and post medication) were abstracted from the hospital database. The post medication spirometry data was analysed. 201 subjects met the criterium of a FER < LLN and were used in the analysis. Severity in obstruction was calculated using an Excel algorithm using the cut-of values as published in both ERS statements ^1,2.
Results: characteristics are shown in table 1. All patients were diagnosed with an obstruction according to the 2005 rules, with the largest group of mild obstruction. Using the 2021 interpretation a shift in severity is visible. A moderate obstruction is the most common value, while a large group of our population is classified as normal (25%).

Conclusion: the 2021 update in general leads to decrease in severity of obstruction. For a substantial proportion of our patients this changes positively their perspective of quality of life and mortality.