Validity and Reliability of a Novel Multimodal Questionnaire for the Assessment of Abdominal Symptoms in People with Cystic Fibrosis (CFAbd-Score).

Abstract

For people with cystic fibrosis, validated patient-reported outcome measures for the assessment of the complex abdominal involvement are lacking. The objective of this study was to examine whether the CFAbd-Score, a novel questionnaire consisting of 28 items, meets the essential requirements (validity and reliability) for a patient-reported outcome measure according to US Food and Drug Administration recommendations. Content validity was assessed by recording the frequencies and severity of symptoms that occurred during the prior 2weeks in patients with cystic fibrosis (n = 116; aged ≥ 6years). Comparing the CFAbd-Score results obtained from patients with cystic fibrosis and healthy controls (n = 88), we determined known-groups validity. To explore the structure of the patient-reported outcome measure, a factor analysis was conducted. Internal consistency of the five extracted score domains was assessed using Cronbach's alpha. For test-retest reliability, a subgroup of patients (n = 43) was reevaluated and intra-class correlation coefficients were determined. The CFAbd-Score differentiated patients with cystic fibrosis from healthy controls with a large effect size (17.3 ± 1.1 vs. 8.0 ± 0.7 points; p < 0.001; Cohen's d = 0.85). Items, domains, and scores reflected the relevance to patients with cystic fibrosis and allowed a differentiation between subgroups of patients with cystic fibrosis (e.g., patients with and without abdominal pain, pancreatic sufficiency, and age groups). High item-domain loadings as well as good to excellent internal consistency and reproducibility (Cronbach's α = 0.70-0.92; intra-class correlation coefficient = 0.932, 95% confidence interval 0.874-0.963) indicated construct validity and reliability. The CFAbd-Score has successfully passed through key steps of the iterative process of patient-reported outcome measure development. Prospectively, the CFAbd-Score is proposed as a patient-centered instrument for monitoring abdominal symptoms and, most interestingly, for evaluating changes in symptoms with novel treatments such as cystic fibrosis transmembrane regulator modulators. ClinicalTrials.gov: NCT03052283.