Validation of a new glucocorticoid-specific Patient-Reported Outcome Questionnaire (the Steroid PRO)

ObjectivesGlucocorticoids used in the treatment of inflammatory rheumatic conditions can impact on health-related quality of life. An underpinning qualitative study developed a long-list of candidate items for a treatment-specific patient-reported outcome (PRO) measure. The objective of this paper is to determine scale structure and psychometric properties of the Steroid PRO.MethodsA cross-sectional survey of adults from the UK, USA, Australia and New Zealand, taking glucocorticoids for a rheumatic disease. Initial survey collected demographics, clinical information, 40 Steroid PRO candidate items and EuroQol-5 Dimensions- 5 levels (EQ-5D-5L). Follow-up, 3-5 days later, collected Steroid PRO candidate items and a condition-change ('transition') question. Analysis included Rasch measurement model, exploratory factor analysis (EFA), and hypothesis testing for discriminative validity, convergence validity and test-retest reliability.ResultsTotal responses 946: UK n=743 (79%); USA n=139 (15%); Australia/New Zealand n=64 (7%); mean age 57.6 (SD=13.6); 833 (88%) women. Participants with inflammatory arthritis n=197 (21%), connective tissue disease and/or vasculitis n=402 (42%), giant cell arteritis and/or polymyalgia rheumatica n=347 (37%). Twenty-five items were removed due to lack of fit to Rasch model. Of the remaining items, EFA suggested four subscales: Social impact (4 items); Impact on appearance (3 items); Psychological impact (5 items); Treatment concerns (3 items). Rasch modelling supported a four-subscale structure and total score, confirming construct validity and reliability. Hypothesis testing confirmed discriminant and convergence validity. Intraclass correlation coefficient (total score) was 0.809 demonstrating excellent (test-retest) reliability.ConclusionsThe Steroid PRO is a 15-item, valid and reliable scale for measuring the impact of glucocorticoid therapy in people with rheumatic diseases.