Spirometric testing. Number of tests required and selection of data.

To address the questions of whether three or five maneuvers for forced vital capacity (FVC) should be required for adequate spirometric testing and whether the largest or mean values for FVC and the forced expiratory volume in the first second (FEV1) should be used for analysis, we analyzed spirometric data obtained from approximately 3,000 people for each of three consecutive years. The following four algorithms for selection of data were tested: (1) the average of the best two of five measurements; (2) the average of the best two of the first three; (3) the best of five; and (4) the best of the first three. There were no significant differences between any two algorithms within a given year and no differences between any two years for any algorithm. We conclude that there is little to be gained by requiring more than three maneuvers for FVC or in using values other than the largest FEV1 and FVC.