Validation of the FACIT-fatigue subscale, selected items from FACT-thrombocytopenia, and the SF-36v2 in patients with chronic immune thrombocytopenia

To assess the validity and reliability of the fatigue subscale of the Functional Assessment of Chronic Illness Therapy (FACIT-F), a 6-item subset from the thrombocytopenia subscale of the Functional Assessment of Cancer Therapy (FACT-Th6) and the Short Form-36 Version 2 (SF-36v2) in 2 clinical trials of the thrombopoietin receptor agonist eltrombopag in chronic immune thrombocytopenia (ITP) patients. In the 6-month, RAndomized placebo-controlled ITP Study with Eltrombopag (RAISE; n = 197), the FACIT-F, FACT-Th6, and SF-36v2 were administered at baseline, day 43, weeks 14 and 26, or early withdrawal. In the ongoing open-label extension study, Eltrombopag EXTENDed Dosing Study (EXTEND; n = 154), measures were administered at baseline, at the beginning of each stage, and at permanent discontinuation of study medication. FACIT-F, FACT-Th6, and SF-36v2 demonstrated acceptable internal consistency reliability (i.e., all Cronbach's alphas > 0.70) and test-retest reliability (all intraclass correlation coefficients > 0.70). Construct validity was supported by moderate (0.35 < r < 0.50) to strong (r > 0.50) inter-measure correlations for baseline and change scores. A small to medium magnitude of effect was captured by the FACIT-F and FACT-Th6 among patients who experienced sustained platelet responses. Results provide support for the validity, reliability, and responsiveness of the FACIT-F, FACT-Th6, and SF-36v2 in chronic ITP patients.