Introduction Treatment decisions for children with asthma are often made in response to changes in lung function. Reproducibility limits may help to distinguish a clinically significant change from ?noise? introduced by age or time. A task force has recently highlighted the merits of FEV₁ change score.  

Aim Derive a change score for FEV₁ in children with asthma.

Methods Spirometry data from five studies in asthma that measured FEV₁ at ~quarterly intervals over one year were collated. A change score (aka conditional z-score for change, Zc) was calculated using standard methodology, taking into account the correlation (r) between paired measurements and both the initial age and time interval (Stanojevic S et.al, Thorax 2020). Exploratory analyses determined how r changed according to demographic and clinical factors (sex, height, weight, level of asthma control, and treatments). We further evaluated whether Zc was associated with between-visit changes in level of asthma control.

Results There were 5,211 FEV₁ measurements from 1,264 individuals aged 4.7-19.0y (mean=12.2y). The asthma-defined Zc was similar to the Zc published in health, (mean Zc: asthma=-0.12; health=-0.05), and it was independent of sex, height, weight, level of asthma control, and treatments. Of 4,339 pairwise measurements where asthma was controlled on both occasions, FEV₁ was within the Zc reproducibility limits (<± 1.96) for 86% of cases; in comparison 74% of cases had <±10% change in FEV₁% predicted.

Conclusions. We have derived a change score for children with asthma.  Zc was comparable between healthy children and children with controlled asthma.  The relationship between Zc and future asthma outcomes needs further investigation.