Natural variability of lung function in young healthy school children

Abstract

Background: Knowledge about long-term variability of lung function in healthy children is essential when monitoring and treating those with respiratory disease over time. Aim: To define the natural variability in spirometry in young children after an interval of twelve months. Methods: The Size and Lung function In Children (SLIC) study was a prospective study designed to assess spirometry and body size, shape and composition in a multi-ethnic population of London school children. Fourteen schools with a wide range of socio-economic circumstances were recruited. Spirometric and anthropometric assessments and parental questionnaires pertaining to respiratory symptoms, previous medical history, pubertal status and socio-economic circumstances were completed at baseline and ~one year later. Findings: Technically acceptable spirometry data on two occasions ~1y apart (range: 9-16months) were available in 758 children (39% boys, mean (SD) age:8.1(1.6)y), 593 of whom were classified as ‘healthy’. Mean (SD) within-subject between-test variability was 0.05 (0.6) z-scores, with 95% of all the children achieving a between-test variability within ±1.2z-scores (equating to ~13%predicted). Interpretation: Natural variations of at least 1.2z-scores occur in healthy children over ~1y. These must be considered when interpreting results from annual reviews in those with lung disease who are otherwise stable if unnecessary further investigations or changes in treatment are to be avoided