INTRODUCTION: Many regulations for aeromedical assessments state that a ratio between forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) of < 0.7 should be evaluated by a pulmonary specialist. The Global Lung Initiative (GLI) reference values introduced the lower limit of normal (LLN 2.5), in which the lowest 2.5% of the population is regarded as abnormal, instead of a fixed ratio. This study assesses the impact of adopting GLI reference values on aeromedical evaluation and referrals.METHODS: The Royal Netherlands Air Force performed 7492 aeromedical assessments between February 2012 and April 2017. Cases with FEV1/FVC < 0.7 from three groups were selected: 1) men < 25 yr; 2) men > 40 yr; and 3) women, with twice as many matched controls. Pearson's Chi-squared and Fisher's exact tests were used to analyze the data.RESULTS: From the database, 23 (group 1), 62 (group 2), and 7 (group 3) cases were selected, with 184 controls. Respectively, 17%, 84%, and 29% would not be referred using the GLI. In the controls, this would lead to one additional referral (group 1). Qualitative analysis of the cases who would not be referred using the GLI showed that no significant diagnoses would have been missed.DISCUSSION: Using the GLI LLN 2.5 reference values for pulmonary function tests leads to significantly fewer referrals to a pulmonary specialist without missing relevant pulmonary pathology in our aircrew. This would reduce resources spent on the assessment of aircrew without compromising flight safety.Wingelaar-Jagt YQ, Wingelaar TT, Bülbül M, vd Bergh PP, Frijters E, Staudt E. The effect of using the lower limit of normal 2.5 in pulmonary aeromedical assessments. Aerosp Med Hum Perform. 2020; 91(8):636-640.