Appraisal and extension of the ERS/ATS Interpretative Strategy for Pulmonary Diffusing Capacity

ABSTRACT The ERS/ATS22 interpretative flowchart classifies diffusing capacity (DLco) into 5 scenarios with associated pathophysiology, and has not been tested on large patient groups. We aimed to obtain a more layered DLco interpretation, by interrogating DLco components Kco and V A , and by estimating lung inflation during the DLco test to identify the presence of restriction, which crucially impacts Kco interpretation. By assessing a “low V A ” against lung inflation, a novel 9-scenario DLco classification with associated pathophysiology can be obtained. Lung patients from a tertiary center were classified according to the ERS/ATS22 chart and the novel 9-scenario one. Besides a control group of healthy subjects (n=303), disease groups under study were the following : asthma (n=1615), COPD (n=1338), CF (n=108), extrapulmonary restriction (n=122), ILD (n=98), post-COVID (n=193). Except for COPD, the prevalence of “normal DLco” (ERS/ATS22) was generally greater than that of “normal V A and normal Kco” (9-scenario); this discrepancy was most marked in CF (81% vs 56%) and in extrapulmonary restriction (57% vs 37%). With the novel 9-scenario chart, patients from very different diagnostic groups with a “low DLco” due to emphysema, bronchial disease, interstitial damage or incomplete expansion got classified across distinct scenarios, whereas ERS/ATS22 just grouped them together. In conclusion, when “low V A ” is evaluated against lung inflation, a differentiation of DLco interpretation can be obtained in various patient groups involving obstruction and/or restriction. This approach can be readily implemented in clinical practice.