Repeatability of Spirometry in 18,000 Adult Patients

The objective of this study was to determine the limits for repeatability of FEV₁, FVC, and PEF during spirometry test sessions in adult outpatients. A retrospective chart review of 18,000 consecutive patients, aged 20 to 90 years, referred to a large outpatient pulmonary function laboratory for testing was performed. Measurements included the differences between the highest and second-highest FVC (dFVC), FEV₁ (dFEV₁), and PEF (dPEF), from prebronchodilator spirometry, and anthropometric factors. Ninety percent of the patients were able to reproduce FEV₁ within 120 ml (6.1%), FVC within 150 ml (5.3%), and PEF within 0.80 L (12%). Patient characteristics, such as sex, age, height, smoking status, and FEV₁ (% predicted), had very little effect on repeatability, explaining only 2 to 4% of the variation in repeatability (expressed in milliliters). We conclude that the ability of patients to meet or exceed spirometry repeatability goals does not depend on patient characteristics when testing is performed by experienced personnel. The current American Thoracic Society repeatability goal of 200 ml for FEV₁ and FVC may be too lenient.