Background: The Stool Frequency (SF) and Abdominal Pain (AP) items from the Crohn's Disease Activity Index are together referred to as the "Patient Reported Outcome" (PRO). The SF item measures the number of very soft/liquid stools and the AP item measures abdominal pain severity, which are common Crohn's disease (CD) symptoms that patients consider important to treat. This study evaluated the psychometric properties of both PRO items separately and estimated thresholds for clinical remission in moderately to severely active CD.
Methods: The measurement properties of the PRO items were analyzed using pooled data from VIVID-1 (NCT03926130), a Phase 3, randomized, placebo- and active-controlled study in adults with moderately to severely active CD. Analyses used weekly average scores of the SF and AP items at Weeks 0 (Baseline), 4, 12, and 52. Remission thresholds were estimated using the Patient Global Rating of Severity (PGRS) and Patient Global Impression of Change (PGIC) as primary anchors as well as qualitative evidence from exit interviews.
Results: Data from 1065 participants (mean age: 36.2 years [standard deviation: 13 years]) were analyzed. During the trial, scores improved for both PRO items. Both items demonstrated moderate-to-good test-retest reliability for participants defined as stable based on PGRS and PGIC. Most correlations of related assessments were moderate (0.30≤|ρ| <0.70) with SF and moderate-to-large (0.30≤|ρ| ≤0.90) with AP. By contrast, as anticipated, both items had weak correlations (|ρ| <0.30) with endoscopic and laboratory assessments. The PRO items could discriminate between groups of participants known to differ based on other assessments. The PRO items were able to detect change, as score changes in both items between Baseline and Weeks 12 and 52 differed significantly between most PGRS and PGIC categories. Anchor-based analyses combined with responses from the exit interviews suggested that an SF score of ≤ 3 and an AP score of ≤ 1 could together represent clinical remission.
Conclusion: These results support the reliability, construct-validity, and responsiveness of both PRO items in moderately to severely active CD and confirm previously suggested scores for both items that could represent clinical remission.
Trial registration: Clinicaltrials.gov, NCT03926130. Registered 23 April 2019, https://clinicaltrials.gov/study/NCT03926130 .
Keywords: Abdominal pain; Crohn’s disease; Patient reported outcome; Psychometric evaluation; Stool frequency.
This study focused on two of the questions (or “items”) from a commonly used questionnaires in Crohn’s disease: the Stool Frequency (SF) item, which counts the number of very soft or liquid stools in a 24-hour period, and the Abdominal Pain (AP) item, which rates severity of abdominal pain in the same time period. We are referring to these two items as the “Patient Reported Outcome” (PRO). This study looked at how well each of these two items did in measuring what they are supposed to measure by using data from people with Crohn’s disease who had participated in a clinical trial. Trial participants answered the SF and AP daily during the trial by using an electronic diary device. Some of the participants were also interviewed to find out when they would consider their disease to be in remission (no longer active). The results showed that both PRO items (SF and AP) can be used by people with Crohn’s disease to accurately measure their very soft or liquid stool frequency and abdominal pain. Further, we estimated which scores on SF and AP could tell us whether someone with Crohn’s disease has achieved remission of their very soft or liquid stools and of their abdominal pain.
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