Reliability and validity of the University of California, Los Angeles scleroderma clinical trial consortium gastrointestinal tract instrument

Abstract

Objective To refine the previously developed scleroderma (systemic sclerosis [SSc]) gastrointestinal tract (GIT) instrument (SSC-GIT 1.0). Methods We administered the SSC-GIT 1.0 and the Short Form 36 to 152 patients with SSc; 1 item was added to the SSC-GIT 1.0 to assess rectal incontinence. In addition, subjects completed a rating of the severity of their GIT involvement (from very mild to very severe). Evaluation of psychometric properties included internal consistency reliability, test–retest reliability (mean time interval 1.1 weeks), and multitrait scaling analysis. Results Study participants were mostly women (84%) and white (81%); 55% had diffuse SSc. Self-rated severity of GIT involvement ranged from no symptoms to very mild (39%), mild (21%), moderate (31%), and severe/very severe (9%). Of an initial 53 items in the SSC-GIT 1.0, 19 items were excluded, leaving a 34-item revised instrument (the University of California, Los Angeles Scleroderma Clinical Trial Consortium GIT 2.0 [UCLA SCTC GIT 2.0]). Analyses supported 7 multi-item scales: reflux, distention/bloating, diarrhea, fecal soilage, constipation, emotional well-being, and social functioning. Test–retest reliability estimates were ≥0.68 and coefficient alphas were ≥0.67. Participants who rated their GIT disease as mild had lower scores on a 0–3 scale on all 7 scales. Symptom scales were also able to discriminate subjects with corresponding clinical GIT diagnoses. The Total GIT Score, developed by averaging 6 of 7 scales (excluding constipation), was reliable and provided greater discrimination between mild, moderate, and severe self-rated GIT involvement than individual scales. Conclusion This study provides support for the reliability and validity of the UCLA SCTC GIT 2.0, an improvement over the SSC-GIT 1.0, and supports a Total GIT Score in SSc patients with GIT.