Pulmonary function testing: sources of error in measurement and interpretation.

Valid pulmonary function data require that attention be paid to issues that can lead to errors in measurement or in interpretation. Routine procedures designed to reduce errors should be established. Among the most important of these are (1) assuring the accurate measurement and calculation of lung function parameters, which requires attention to accuracy when an instrument is brought into service in a laboratory and again when it is updated; (2) selecting reference equations and lower limits of normal appropriate for the patients being studied and for the equipment being used; (3) avoiding the errors introduced by using an excessive number of measurements in generating an interpretation; and (4) avoiding interpretation of results without considering the clinical setting and the pertinent elements of a complete data base.