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. However, this recommendation is based upon a single study from 1999, which was limited to White patients, and used race-specific reference equations that are no longer recommended by ERS/ATS. We sought to reassess the support for this recommendation by calculating the negative predictive value (NPV) of a normal FVC in a diverse, multicenter cohort using race-neutral reference equations.

We interpreted PFTs performed between 2000 and 2023 in two academic medical systems and in a national electronic health record (EHR) database. We calculated the NPV of a normal FVC to exclude restriction overall and among pre-specified racial and ethnic groups.

We included PFTs from 85990 patients. The prevalence of restriction was 35.1%. The overall NPV of a normal FVC to exclude restriction was 80.5% (95% CI 80.1% to 80.8%), compared to an NPV of 97.6% cited in support of ERS/ATS guidelines. The NPV ranged from 65.2% (95% CI 64.4% to 66.0%) among non-Hispanic Black patients to 85.9% (95% CI 85.6% to 86.3%) among non-Hispanic White patients. This difference was largely attributable to lower FVC z-scores among non-Hispanic Black patients.

The NPV of a normal FVC is lower than has been previously reported and varies by race and ethnicity. The approach to PFT interpretation recommended by ERS/ATS guidelines results in the under-recognition of restriction, particularly among non-Hispanic Black patients.