Background The National Institutes of Health PROMIS® roadmap initiative is a cooperative research program designed to develop, evaluate, and standardize item banks to measure patient-reported outcomes (PROs) across different medical conditions as well as the US general population (US GP). PROMIS includes items banks that assess self-reported physical, mental, and social health.
Objectives (i) To develop GI Symptoms item bank applicable to patients with GI illness and (ii) To evaluate the construct validity of the PROMIS GI item bank in SSc.
Methods A systematic review was conducted to find relevant articles assessing PROs in GI diseases and a conceptual model was proposed. The individual items from extant instruments were grouped based on different symptoms. This was complemented by 12 focus groups including 102 patients with GI conditions to evaluate their symptoms. New items were developed based on extant items and input from the focus group participants followed by cognitive debriefing in 28 patients with GI conditions. Items were finalized based on psychometric analyses including categorical confirmatory factor analyses and item response theory modeling to estimate item thresholds and discrimination parameters. 167 patients with SSc were administered the PROMIS GI item banks and the UCLA Scleroderma Clinical Trials Consortium Gastrointestinal Scale (GIT 2.0) instrument. GIT 2.0 is a multi-item instrument that measures GI symptoms in SSc. Product-moment correlations and a multitrait-multimethod analysis of the PROMIS GI scales with the GIT 2.0 symptoms scales were used to evaluate convergent and discriminant validity.
Results 102 items were developed after qualitative analysis (N=130 patients) and administered to 865 patients with GI conditions and 1177 participants from the US GP. Confirmatory factor analyses provided support for 8 scales: Gastroesophageal reflux (13 items), disrupted swallowing (7 items), diarrhea (5 items), bowel incontinence/soilage (4 items), nausea and vomiting (4 items), constipation (9 items), belly pain (6 items), and gas/bloat/flatulence (12 items). All scales were calibrated using the two-parameter IRT graded response model and scored on a T-score metric with a mean of 50 and SD of 10 in the US general population (GP). Patients with SSc GI involvement had PROMIS GI scale scores 0.2-0.7 SD worse than US population. Correlations among scales measuring the same domains for the PROMIS GI and GIT 2.0 measures were large ranging from 0.61 to 0.87 (average r=0.77). The average correlation between different symptom scales was 0.22, supporting discriminant validity.
Conclusions Using NIH PROMIS framework, we have developed a 60-item GI Symptoms scale that can be used for clinical care and trials. This study also provides support for the construct validity of the PROMIS GI scales in SSc. Future research is needed to assess the responsiveness to change of these scales in patients with SSc.
Disclosure of Interest V. Nagaraja Employee of: Salary support from the United States Department of Veterans Affairs., B. Spiegel: None declared, R. Hays Grant/research support: NIH/NIA Grants P30-AG028748 and P30-AG021684, and NCMHD Grant 2P20MD000182, P. Khanna: None declared, L. Chang: None declared, G. Melmed: None declared, R. Bolus: None declared, D. Khanna Grant/research support: NIH/NIAMS K24 AR063120-02