Objectives: If reference values do not accurately reflect the distribution of lung function in the population, the interpretation of spirometry results may be incorrect. Differences in lung function exist between populations, which supports the use of local reference values. In Finland, the national reference values for spirometry are currently in use. The aim of this study was to assess the correlation between measured spirometric values from healthy adults and the reference values used in Finland.
Methods: In the present population-based study, spirometry results were assessed in healthy adults aged 21 to 70 years in northern Finland. After exclusions for any chronic pulmonary disease or symptom, 206 men and 215 women remained in the group. We calculated regression equations for spirometric reference values in adults and compared these with European recommendations, and with the reference values currently used in Finland.
Results: These comparisons revealed large differences. The linear models do not take into account the physiological changes in both young and old adults and, thus, the reference values calculated according to the European recommendations differed from the real measured results at both ends of the 20- to 70-year age scale. Moreover, values from the logarithmic Finnish reference equations also diverged from our measurements; the differences were largest in subjects younger than 30, and in elderly men.
Conclusion: Differences between populations and reference equations make international comparisons difficult, and divergence between reference values and real results may lead to incorrect clinical interpretation.