Psychometric validation of the SF-36 Health Survey in light chain amyloidosis: results from community-based and clinic-based samples

BACKGROUND: Light chain (AL) amyloidosis, a rare and life-threatening protein misfolding disorder, causes organ damage and severely impacts health-related quality of life (HRQoL). No patient-reported outcome (PRO) HRQoL measure has been validated for use in an AL amyloidosis patient population, leaving a gap for researchers conducting observational studies and clinical trials for drug development. The SF-36 Health Survey (SF-36) has been the most frequently used PRO in AL amyloidosis studies to date, and early qualitative validation studies support its use in this population. The aim of this study was to assess the psychometric properties of the SF-36 among patients with AL amyloidosis. METHODS: Data from community-based (n=341) and clinic-based (n=1,438) observational studies were used to document the psychometric properties of the SF-36 in this disease population. Reliability was estimated using internal consistency (Cronbach’s alpha) and test–retest reliability (intraclass correlation). Convergent validity, known-groups validity, and the ability to detect change were assessed with available criterion variables. RESULTS: Scale reliability (Cronbach’s alpha ≥0.780 for all scores) and test–retest reliability (intraclass correlation coefficients ≥0.731 for all) were acceptable. Scale convergent validity was supported by strong correlations with conceptually related measures. Mean SF-36 scores varied by response to treatment (P<0.05 for all scores) and a self-reported measure of disease severity (P<0.001 for all scores). Data indicate that the SF-36 is sensitive to changes in other measures over time. CONCLUSION: This study provided clear and consistent evidence of the psychometric properties of the SF-36 in both community-based and clinic-based samples of patients with AL amyloidosis.