Lung function measurement in general practice. General practice measurements compared with laboratory measurements during the DIMCA trial.

The mean decline in lung function was: -0.037 l/year [95% confidence interval (CI) -0.202 to 0.129] from LFL data and -0.027 l/year (95% CI -0.242 to 0.188) from GPS data. The mean intra-individual difference was -0.0025 l (95% CI -0.493 to 0.488 l). The test characteristics of the spirometer used in GPS did not meet all of the American Thoracic Society guidelines; in particular, the random error was too large. The difference in assessments between measurement in LFL and GPS were such that misclassification might occur if slopes were calculated. CONCLUSIONS. :Repeated measurement in this study showed that GPS measurements are not interchangeable with LFL measurements. Therefore, one has to be cautious when interchanging lung function data from an LFL and a GPS.