Reference equations for pulmonary function tests in preschool children: a review

Recent developments in pulmonary function tests (PFTs) in preschool children (2-5 years of age) have meant that objective assessments of respiratory function are now possible for this age group. However, the application and interpretation of these tests may be limited by the relative paucity of appropriate reference equations. This review summarizes available preschool reference equations, identifies the current gaps and limitations in the methodologies and statistics used and proposes future directions for improving reference data. A PubMed search which included the MeSH terms (preschool [2-5years]), (respiratory function test), and (reference value) yielded 214 publications which were screened to identify 34 publications presenting 36 reference equations for seven techniques. There were considerable differences with respect to population characteristics, recruitment strategies, equipment and methodologies and reported parameters both within and between each measurement technique. Despite an increasing number of reference equations for PFT for preschool children, the extent to which these can be generalized to other populations may be limited in some cases by inclusion of relatively few children less than 5 years of age, a lack of details regarding the sample populations and measurement techniques and/or inappropriate statistical analysis. A fresh approach based on large sample sizes, clearly documented population characteristics, equipment and protocols, and more rigorous modern statistical methods both for developing reference equations and interpreting results could enhance clinical application of these tests. This in turn would maximize the tremendous opportunities to detect early lung disease offered by the recent surge in developing suitable tests for preschool children.