A normal forced vital capacity does not reliably or equitably exclude restriction

European Respiratory Society and American Thoracic Society (ERS/ATS) guidelines for pulmonary function test (PFT) interpretation recommend the use of a normal forced vital capacity (FVC) to exclude restriction. According to these guidelines, static lung volume measurements are needed to determine the presence or absence of restriction only if the FVC is abnormal. If the FVC is normal, restriction can be excluded on the basis of spirometry alone. In support of this recommendation, these guidelines cite a single study which estimated the negative predictive value (NPV) of the FVC lower limit of normal (LLN) to be 97.6%. This study, however, involved fewer than two thousand PFTs performed at a single pulmonary diagnostic lab, included only White patients, and employed race-specific reference equations that are no longer recommended by ERS/ATS. While subsequent studies have provided similar NPV estimates, these studies have also been limited to small cohorts of patients tested at a single site. Moreover, no study has assessed the impact of the adoption of the race-neutral Global Lung Function Initiative (GLI) Global reference equations on the NPV, despite the significant effect these equations have on the FVC LLN.

We sought to evaluate the validity and equity of current ERS/ATS guidelines by reassessing the NPV of the FVC LLN, applying race-neutral reference equations to a large, diverse, multi-center cohort.

National Heart, Lung, and Blood Institute

Alexander T Moffett, Aparna Balasubramanian, Meredith C McCormack, Jaya Aysola, Scott D Halpern, Gary E Weissman