Pulmonary function tests: comparison of 95th percentile-based and conventional criteria of normality.

Background: Although 95th percentile-based normal limits are recommended instead of conventional criteria of normality to guide pulmonary function test (PFT) readings, we have found no objective assessment of how the choice of normal limits might influence PFT interpretation.

Methods: We did a retrospective comparison of PFT readings referenced to conventional criteria of normality versus independent repeat assessments influenced by 95th percentile-based normal limits in 166 veterans. We also conducted a nationwide telephone survey of VA Hospital PFT laboratories.

Results: Discordant readings occurred in only 7.2% of 616 individual PFTs; however, these discrepancies could potentially influence at least one component of the PFT report of 26.5% of our subjects. The 95th percentile-based normal limits were used by only 40% of VA PFT laboratories, without relationship to geography or hospital size.

Conclusions: Discrepancies between 95th percentile-based and conventional normal limits can potentially influence PFT readings, and 95th percentile-based criteria are not used in the majority of VA PFT laboratories.