Comparing Proxy, Adolescent and Adult Assessments of Functional Ability in Adolescents with Juvenile Idiopathic Arthritis

OBJECTIVE: In pediatric research, investigators rely on proxy reports of outcome, such as the proxy-completed Childhood Health Assessment Questionnaire (C-HAQ), to assess function in juvenile idiopathic arthritis (JIA). As children mature, they may self-complete the adult HAQ or the unvalidated adolescent-specific C-HAQ. It is unclear how these measures compare and whether they are directly interchangeable. The present study was undertaken to compare agreement between the proxy-completed C-HAQ, adolescent-specific C-HAQ, and the HAQ at initial presentation to pediatric rheumatologic care and 1 year following the first presentation in adolescents with JIA. METHODS: Adolescents ages 11-17 years participating in the Childhood Arthritis Prospective Study (CAPS), a UK multicenter inception cohort, were included. In a CAPS substudy, adolescents self-completed the adolescent-specific C-HAQ and the HAQ, and proxies simultaneously completed the proxy-completed C-HAQ at baseline and 1 year. Correlation and agreement between scores were assessed at baseline. Agreement and ability to similarly classify clinically important changes over time were assessed at 1 year following initial presentation to rheumatologic care. RESULTS: A total of 107 adolescents (adolescent-specific C-HAQ and HAQ) or their proxies (proxy-completed C-HAQ) had completed all 3 measures at baseline. Median age at diagnosis was 13 years, and 61% were female. Although the 3 scores demonstrated strong correlations (r > 0.8), they were not completely interchangeable, with agreement ranging between 70% and 80%. There was similar agreement between the changes in scores between baseline and 1 year. Using proxy-completed C-HAQ minimum clinically important cutoffs, the adolescent-specific C-HAQ and the HAQ similarly classified 80% to 90% of adolescents as having improved or worsened. CONCLUSION: While there is relatively high agreement and similar classification of change between HAQ and the 2 C-HAQ scores, these are not completely interchangeable. This impacts the comparison of function when measured in different ways over the lifespan.