Validity, Reliability, and Responsiveness of a New Measure of Health-Related Quality of Life in Children with Immune Thrombocytopenic Purpura: The Kids’ ITP Tools

OBJECTIVE: To refine the disease-specific health-related quality of life measure in immune (idiopathic) thrombocytopenic purpura (ITP) and to determine its validity, reliability, and responsiveness to change. STUDY DESIGN: The initial phase involved cognitive debriefing of 12 families, on the basis of which the measure was modified and then named Kids' ITP Tools (KIT). The measure was administered on 2 occasions with the Pediatric Quality of Life Inventory (PedsQL) to 41 patients with acute ITP and 49 patients with chronic ITP, 2 to 18 years old, and their parents (proxy-respondents) at 6 North American centers. RESULTS: Patients with acute ITP had lower scores when compared with patients with chronic ITP (child 64 versus 76, proxy 69 versus 77). The KIT moderately correlated with the PedsQL. Child versus proxy KIT scores showed moderate correlation, and the KIT was superior to the PedsQL. Test-retest reliability was substantial in the child report, but only moderate for the proxy report, similar to the PedsQL. The KIT showed a mean score change of 13 in the child and 15 in the proxy, which was greater than the PedsQL child's change of 7 and proxy change of 5. CONCLUSION: The KIT is valid, with good distinction between acute and chronic ITP and a moderate correlation with the PedsQL. The KIT demonstrated reliability comparable with that of the PedsQL, yet it was more responsive to change. Therefore the KIT can be used as an outcome measure in future clinical trials of childhood ITP.