Measurement properties of the Short Form-36 (SF-36) and the Functional Assessment of Cancer Therapy - Anemia (FACT-An) in patients with anemia associated with chronic kidney disease

Fredric O. Finkelstein, Floortje van Nooten, Ingela Wiklund, Dylan Trundell, David Cella

Anemia is a common and debilitating manifestation of chronic kidney disease (CKD). Data from two clinical trials in patients with anemia of CKD were used to assess the measurement properties of the Medical Outcomes Survey Short Form-36 version 2 (hereafter SF-36) and the Functional Assessment of Cancer Therapy-Anemia (FACT-An). The Vitality and Physical functioning domains of the SF-36 and the FACT-An Total, Fatigue and Anemia subscales were identified as domains relevant to CKD-associated anemia. A total of 204 patients aged 18-80 years were included in the analyses that included internal consistency (Cronbach's alpha), test-retest reliability (intraclass correlation coefficients [ICCs]), convergent and known-groups validity, responsiveness, and estimates of important change. Both the SF-36 and the FACT-An had strong psychometric properties with high internal consistency (Cronbach's alpha: 0.69-0.93 and 0.79-0.95), and test-retest reliability (ICCs: 0.64-0.83 and 0.72-0.88). Convergent validity, measured by correlation coefficients between similar concepts in SF-36 and FACT-An, ranged from 0.52 to 0.77. Correlations with hemoglobin (Hb) levels were modest at baseline; by Week 9, the correlations with Hb were somewhat higher, r = 0.23 (p < 0.05) for SF-36 Vitality, r = 0.22 (p < 0.05) for FACT-An Total, r = 0.26 (p < 0.001) for FACT-Fatigue and r = 0.22 (p < 0.01) for Anemia. Correlations with Hb at Week 13/17 were r = 0.28 (p < 0.001) for SF-36 Vitality and r = 0.25 (p < 0.05) for Role Physical; FACT-An Total correlation was r = 0.33 (p < 0.0001), Anemia was r = 0.28 (p < 0.001), and Fatigue was r = 0.30 (p < 0.001). The SF-36 domains and Component Summary scores (p < 0.05-p < 0.0001) demonstrated ability to detect change. For the FACT-An, significant differences (p < 0.05-p < 0.0001) were observed between responder and non-responder change scores: important change score estimates ranged from 2 to 4 for Vitality and 2-3 for Physical functioning. Important change scores were also estimated for the FACT-An Total score (6-9), the Anemia (3-5), and Fatigue subscale (2-4). Both the SF-36 Vitality and Physical function scales and the FACT-An Total, Fatigue and Anemia scales, are reliable and valid measures for assessing health-related quality of life in anemia associated with CKD.