INTRODUCTION: The National Health Service for England Long Term Plan identifies respiratory disease as one of its priority workstreams. To assist with earlier and more accurate diagnosis of lung disease they recommend improvement in delivery of quality-assured spirometry. However, there is a likelihood that patients will present with abnormal gas exchange when spirometry results are normal and therefore there will be a proportion of patients whose time to diagnosis is still protracted. We wished to determine the incidence rate of this occurring within our Trust. METHODS: A retrospective review of all patients attending the lung function laboratory for their first pulmonary function assessment from June 2006 to December 2020 was undertaken. Forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) >-1.64 standardised residual (SR) was used to confirm no obstructive lung function abnormality and FVC >-1.64 SR to confirm no suggestion of a restrictive lung function abnormality. Lung gas transfer for carbon monoxide (TLCO) and transfer coefficient of the lung for carbon monoxide (KCO) <-1.64 SR confirmed the presence of a gas exchange abnormality. Spirometry and gas transfer reference values generated by the Global Lung Initiative were used to determine normality. RESULTS: Of 12 835 eligible first visits with normal FEV1/FVC and FVC, 4856 (37.8%) were identified as having an abnormally low TLCO and 3302 (25.7%) presenting with an abnormally low KCO. Of 3494 with FEV1/FVC SR <-1.64, 3316 also had a ratio of <0.70, meaning 178 (5%) of patients in this cohort would have been misclassified as having obstructive lung disease using the 0.70 cut-off recommended by the Global Initiative for Chronic Obstructive Lung Disease for diagnosing obstructive lung disease. DISCUSSION: In conclusion, to assist with ensuring more accurate and timely diagnosis of lung disease and enhance patients' diagnostic pathway, we recommend the performance of lung gas transfer measurements alongside spirometry in all healthcare settings. To assess and monitor gas transfer at the earliest opportunity we recommend this is implemented into new models being developed within community hubs. This will increase the identification of lung function abnormalities and provide patients with a definitive diagnosis earlier.