Content validation of two SF-36 subscales for use in type 2 diabetes and non-dialysis chronic kidney disease-related anemia

Purpose This study aimed to evaluate the relevance and importance of two SF-36 subscales, Vitality (VT) and Physical Function (PF), to assess concepts of energy and physical function in patients with type 2 diabetes mellitus (DM) and non-dialysis CKD-related anemia. Methods Patients with clinical history of DM and nondialysis CKD-related anemia (n = 68) were identified as follows: 40 participated in concept elicitation (CE) interviews; 20 in cognitive interviews (CI), and 8 in pilot interviews. Relevance and importance ratings for SF-36 VT and PF items were obtained. Interviews were recorded, transcribed, and patient expressions of concepts coded. Interrater agreement was used to evaluate coding consistency. Concepts elicited were mapped to SF-36 VT and PF items. Results Patients (n = 64) were 65.6% women, 42.2% Caucasian, with mean age of 66.1 ± 11.6 years. Of 830 coded concepts, 388 (47%) were "Energy" expressions and 287 (35%) were "PF limitations" expressions. Low energy was reported by 85% patients and rated as an important limitation by 88%. Limitations in PF were reported by 56-82% patients and rated important by 44-96%. CE and CI quotes correspond well to SF-36 VT and PF items. Conclusion SF-36 VT and PF contents were suitable for assessing energy and physical function limitations, respectively, in this patient population.