Quality of life in coeliac disease: item reduction, scale development and psychometric evaluation of the Coeliac Disease Assessment Questionnaire (CDAQ)

Background: A better understanding of coeliac disease can be achieved by assessing health-related quality of life alongside clinical factors. Existing patient-reported outcome measures (PROMs) evaluating quality of life in coeliac disease have not been developed in accordance with the US Food and Drug Administration guidelines.

Aim: To develop a PROM in accordance with best practice guidelines, capturing all aspects of quality of life important to adults with coeliac disease.

Methods: Candidate items for the Coeliac Disease Assessment Questionnaire (CDAQ) were refined through item appraisal, expert review, cognitive interviews, and a translatability assessment. A cross-sectional survey determined further item reduction and the CDAQ's structure. The final CDAQ was administered alongside the Short Form Health Survey Version 2 (SF?36v2) in a second survey to assess construct validity and test-retest reliability.

Results: Pre-testing the 64 candidate items revealed a range of issues which guided their refinement and reduction, resulting in the final CDAQ with 32 items representing 5 subscales: stigma (eight items), dietary burden (eight items), symptoms (five items), social isolation (five items), and worries and concerns (six items). Cronbach's alpha ranged between 0.82 and 0.88 for all domains. Further results showed CDAQ scores were more strongly correlated with the SF-36v2's mental health dimensions, as expected. Intraclass correlation coefficients ranged from 0.79 to 0.89.

Conclusion: The CDAQ is a reliable and valid coeliac-specific measure that captures all aspects of quality of life important to adults with coeliac disease. Further work is underway to assess the CDAQ's responsiveness to change.