Reliability and validity of the Transthyretin Amyloidosis - Quality of Life (ATTR-QOL) Questionnaire impact scales.

Background: The diversity of disease phenotypes associated with transthyretin (ATTR) amyloidosis poses challenges for measurement of health outcomes. The Transthyretin Amyloidosis - Quality of Life (ATTR-QOL) Questionnaire is a disease-specific patient-reported outcome (PRO) measure of the symptoms and impacts of ATTR amyloidosis. The objective of this study was to evaluate the structural validity, reliability, and construct validity of the ATTR-QOL Impact scales.

Methodology: This was a non-interventional, online survey study of adults with self-reported diagnosis of symptomatic ATTR amyloidosis. The survey included the ATTR-QOL and additional criterion measures. A scoring algorithm was proposed and tested. Factor structure, differential item functioning, and psychometric properties were explored.

Results: The analytic sample included 233 patients. Satisfactory fit was found for a 4-factor model of disease impacts (including Daily Activities, Physical Functioning, Social/Role Functioning, and Emotional Wellbeing) and a scoring algorithm was developed. Twelve impact items were dropped from the ATTR-QOLv2 as a result of factor and differential item functioning analyses. Each scale showed evidence of satisfactory internal consistency reliability (Cronbach's α range = 0.85-0.97) and test-retest reliability at 1 week (intraclass coefficient range = 0.84-0.97). Convergent validity was supported by correlations ≥ 0.30 between ATTR-QOL Impact scale scores and other PRO measures of related constructs. The ATTR-QOL Impact scales showed greater impact among patients with worse symptom severity, cardiac functioning, or unemployment due to ATTR amyloidosis (all p < 0.05), supporting known-groups validity.

Conclusion: The ATTR-QOL is a reliable and valid measure of impacts meaningful to patients with ATTR amyloidosis. This study resulted in updates to the ATTR-QOL for item reduction and the development of a scoring algorithm. Ongoing studies are collecting data to evaluate the symptom scales of the ATTR-QOL.