PURPOSE: To assess practice patterns, especially choice of reference equations, interpretive strategies, and the criteria used to define physiologic abnormality for spirometry, lung volumes and diffusing capacity among a geographic sample of pulmonary function testing (PFT) laboratories
METHODS: PFT laboratory directors in 17 hospitals (near Cleveland, Ohio) were surveyed from 9/15/10 to 1/5/11. The survey assessed features of the laboratory, including equipment used, types of tests offered, volume of testing, reference equations used, and the interpretive strategies employed (e.g., regarding how normal was determined, how tests were actually read, etc.).
RESULTS: Responses were received from all 17 laboratories. Great variation was observed not only in the choice of a reference equation for spirometry, but also regarding the criteria used to define airflow obstruction. Great variation was also observed in the use of reference equations for lung volumes and diffusing capacity, as well as the criteria used to define physiologic derangements, like restriction, hyperinflation, air trapping, and impaired diffusion capacity. Five of the 17 laboratories noted reporting the “lower limit of normal” (LLN) in reports, of which 3 reported using LLN to define PFT abnormality. Other definitions of abnormality included values below 70% predicted or 80% predicted.
CONCLUSIONS: This survey demonstrated substantial variation in PFT laboratory practices, including the choice of reference equations, the criteria used to define abnormality, and the strategies for interpreting tests. The degree of variation raises concern about the consistency of results interpretation between laboratories and emphasizes the value of compliance with official guidelines to encourage standardization.
CLINICAL IMPLICATIONS: Because reference equations and interpretive strategies (i.e., the definition of abnormality, strategies for interpreting pulmonary function tests, etc.) varied greatly, these results raise concern that the interpretation of pulmonary function test results could differ across laboratories. These observations underscore the importance of standardization and of PFT laboratory directors’ being fully aware of technique decisions and optimal practice.
DISCLOSURE: The following authors have nothing to disclose: Manish Mohanka, Kevin McCarthy, Meng Xu, James Stoller
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