Measurement characteristics of the childhood Asthma-Control Test and a shortened, child-only version.

The childhood Asthma-Control Test (C-ACT) is validated for assessing asthma control in paediatric asthma. Among children aged 4-11 years, the C-ACT requires the simultaneous presence of both parent and child. There is an unmet need for a tool that can be used to assess asthma control in children when parents or caregivers are not present such as in the school setting. We assessed the psychometric properties and estimated the minimally important difference (MID) of the C-ACT and a modified version, comprising only the child responses (C-ACTc). Asthma patients aged 6-11 years (n=161) from a previously completed multicenter randomised trial were included. Demographic information, spirometry and questionnaire scores were obtained at baseline and during follow-up. Participants or their guardians kept a daily asthma diary. Internal consistency reliabilities of the C-ACT and C-ACTc were 0.76 and 0.67 (Cronbach's α), respectively. Test-retest reliabilities of the C-ACT and C-ACTc were 0.72 and 0.66 (intra-class correlation), respectively. Significant correlations were noted between C-ACT scores and ACQ scores (Spearman's correlation r=-0.56, 95% CI (-0.66, -0.44), P<0.001). The strength of the correlation between C-ACTc scores and ACQ scores was weaker (Spearman's correlation r=-0.46, 95% CI (-0.58, -0.33), P<0.001). We estimated the MID for the C-ACT and C-ACTc to be 2 points and 1 point, respectively. Among asthma patients aged 6-11 years, the C-ACT had good psychometric properties. The psychometric properties of a shortened child-only version (C-ACTc), although acceptable, are not as strong.