[Contemporary interpretation of lung function test results].

OBJECTIVE: To determine which changes take place in the interpretation of spirometric examination results when the transition is made from reference values for children (Zapletal) and adults (European Community for Steel and Coal (ECSC)) to those from the Global Lung Function Initiative (GLI).

DESIGN: Retrospective study.

METHOD: We analysed spirometric data (forced expiratory volume in 1 s, FEV1 and forced vital capacity, FVC) obtained pre- and post-bronchodilation in patients: 1012 children (aged 6-17 years, 47.1% girls) and 4653 adults (aged 18-91 years, 48.6% females). Prevalence rates of airway obstruction based on the lower limit of predicted values (FEV1/FVC < 5th percentile) and an abnormally low FVC (FEV1/FVC > 0.85, FVC < 5th percentile) were calculated in 9 groups of patients. Airway obstruction was also classified based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criterion: FEV1/FVC < 0.70.

RESULTS: Predicted values for FEV1 and FVC according to ECSC and Zapletal were too low. The prevalence rates of spirometrically determined airway obstruction using the three prediction equations varied little; an abnormally low FVC occurred more frequently, especially in young adults. GOLD-defined airway obstruction led to 13.5% underdiagnosis in those aged < 45 years, and about 33% overdiagnosis in elderly subjects, being markedly age-dependent.

CONCLUSION: The prevalence rate of spirometrically determined airway obstruction is little affected by adopting the GLI reference values. The GOLD criterion for airway obstruction leads to underdiagnosis in adults aged < 45 years, and appreciable overdiagnosis in those aged > 45 years. Using z-scores to interpret test results removes biases related to age, height and sex and ethnic group and is clinically valid.