Spirometric variability in a longitudinal study of school-age children.

OBJECTIVES: To describe spirometric reproducibility in a longitudinal study of students from Mexico City, and also the frequency of subjects fulfilling quality criteria proposed for children. SUBJECTS AND METHODS: Three thousand three hundred forty-seven participants from the third through sixth grades of elementary school were recruited to perform biannual spirometry, yielding a maximum of seven evaluations and a total of 15,563 tests. Standard recommendations of the American Thoracic Society (ATS) were followed, using dry rolling-seal volume spirometers.
RESULTS: During their first spirometric test, > 95% of the subjects fulfilled each of the quality criteria proposed by ATS for adults, though not all of them did so simultaneously. For example, only 72.4% obtained three acceptable maneuvers, reproducibility for FEV(1) and FVC to < 200 mL, and a small back-extrapolated volume that increased to 92.3% by the second test. Between phase 1 and phase 7 of the study, spirometry quality increased significantly, as a result of subject and technician training. Intratest and intertest (with a 6-month difference) spirometric variability was less in boys than in girls. Intratest variability was also lower in younger and taller subjects. Technicians contributed significantly to intratest and intertest variability, the latter decreasing if the same technician performed both evaluations.
CONCLUSION: Children > 7 years old can fulfill ATS criteria of quality after the first spirometric evaluation. To maintain quality of spirometric tests in longitudinal studies of children, a strict control is required, especially of technician performance.