PSY3 PSYCHOMETRIC VALIDATION OF FACIT-FATIGUE IN SYSTEMIC LUPUS ERYTHEMATOSUS

Abstract

The Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) PRO measure assesses fatigue, a common symptom experienced in systemic lupus erythematosus (SLE). This study presents evidence on the psychometric properties of FACIT-Fatigue based on data analyses from randomized clinical trials (RCTs) of SLE treatment. Data (GSK study 209013) were obtained from three published belimumab RCTs. Cronbach’s alpha and intraclass correlation coefficient (ICC) were used to evaluate internal consistency and test-retest reliability, respectively, with values ≥0.70 corroborating these properties. Convergent validity was evaluated by computing correlations between FACIT-Fatigue scores and SELENA-SLE Disease Activity Index (SELENA-SLEDAI], annualized flare rate, British Isles Lupus Assessment Group (BILAG) General and Musculoskeletal, and SF-36v2. Known-groups validity was tested by evaluating differences in mean FACIT-Fatigue scores across groups differing in SELENA-SLEDAI (<6, 6–9, ≥10), Physician’s Global Assessment (PGA; none/mild; moderate; severe), or BILAG Musculoskeletal and General (A/B vs C/D/E). Ability to detect changes in SLE was tested by correlating changes in FACIT-Fatigue, SF-36v2, SELENA-SLEDAI, and PGA scores. Mean change in FACIT-Fatigue was compared across the following groups: improved versus same/worse in PGA; BILAG response ≥50% versus <50% of assessments. Cronbach’s alpha exceeded minimum acceptable standards (≥0.94 all time points), as did ICC for test-retest reliability (0.76<ICC<0.92 across trials). Correlations were moderate-strong with SF-36v2 scores (0.49≤|r|≤0.86); low-moderate with BILAG (0.19≤|r|≤0.45), and low with SELENA-SLEDAI and SLE flares rate (|r|<0.25). Mean FACIT-Fatigue scores differed significantly (p≤0.003) across criterion groups. Changes in FACIT-Fatigue scores were at least moderately correlated in the expected direction with SF-36v2 changes (0.42<|r|<0.67), p<0.001) and weakly with changes in SELENA-SLEDAI and PGA (|r|<0.30, p<0.001). Improvement in FACIT-Fatigue scores was significantly greater (p<0.001) among patients with improved PGA and those with BILAG response rates ≥50%. FACIT-Fatigue has strong internal consistency reliability, good test-retest reliability, and strong convergent validity for use in patients with SLE.