Because many different reference equations are available for pulmonary function testing (PFT), and because different interpretive strategies could affect the interpretation of results, we assessed the variation in practice among 17 PFT laboratories.
PFT laboratory directors/supervisors in 17 hospitals (near Cleveland, Ohio) were surveyed between September 15, 2010, and January 5, 2011. The survey assessed the features of the laboratory, including equipment used, types of tests offered, volume of testing, reference equations used, and interpretive strategies employed (eg, how normal was determined, how tests were actually read, and so forth).
Responses were received from all 17 laboratories and were verified using submitted sample PFT reports. The daily median number of tests performed and patients evaluated were 16 and six, respectively. Great variation was observed not only in the choice of reference equations for spirometry, but also in the criteria used to define airflow obstruction. Great variation was also observed in the reference equations used for lung volumes and diffusing capacity, as well as in the criteria used to define physiologic derangements such as restriction, hyperinflation, air trapping, and impaired diffusing capacity. Only three of the 17 laboratories reported and used the “lower limit of normal” to define PFT abnormality.
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 the interpretation of results among laboratories and emphasizes the value of compliance with official guidelines to drive standardization.