Qualitative and quantitative validation of the FACIT-fatigue scale in iron deficiency anemia

BACKGROUND Fatigue is a burdensome symptom in iron deficiency anemia (IDA). To capture the severity and impact of fatigue appropriately it must be measured using validated scales. This study evaluated the content validity and psychometric validity of the Functional Assessment of Chronic Illness Therapy - fatigue scale (FACIT-fatigue) in IDA patients. METHODS Qualitative patient interviews were conducted in the United States to evaluate content validity. The psychometric properties of the FACIT-fatigue scale were investigated using data from a phase 3 clinical trial assessing ferumoxytol in patients with a history of unsatisfactory oral iron therapy or in whom oral iron cannot be used. The statistical analysis assessed the acceptability, reliability, validity and responsiveness of the FACIT-fatigue scale. RESULTS Qualitative interviews showed that fatigue is a central concern to IDA patients and that the FACIT-fatigue scale sufficiently assessed this construct. Psychometric assessment demonstrated that the FACIT-fatigue scale was stable over time (ICC = 0.87) and internally consistent (α = 0.93). The scale demonstrated convergence with other conceptually relevant scales such as SF-36 Vitality (r = 0.74), and distinguished between known groups [i.e., treatment arms (mean difference (95 % CI) = 3.56 (1.68, 5.43), p <0.001) and high vs. low hemoglobin groups (mean difference (95 % CI) = 5.51 (8.59, 2.44) p <0.001)]. Responsiveness was also demonstrated; significant improvements in FACIT-fatigue scale scores corresponded with significant differences between minimal, moderate, and much improved vitality cohorts (p < 0.05). CONCLUSIONS This research demonstrated that the FACIT-fatigue scale has sound measurement properties and is an appropriate and interpretable assessment of fatigue among IDA patients with various underlying conditions.