CF tummy tracker: a cystic fibrosis-specific patient-reported outcome measure for daily gastrointestinal symptom burden

To develop a cystic fibrosis (CF)-specific patient-reported outcome measure (PROM) to measure the daily burden of gastrointestinal symptoms for people with cystic fibrosis (pwCF) aged 12 years and older and address the lack of validated outcome measures for gastrointestinal symptoms in CF. CF Tummy Tracker was developed through a 5-stage approach in accordance with regulatory guidance. This included development and refinement of a conceptual framework; item generation; refinement; reduction; selection; and initial PROM testing. A mixed-methods approach, consisting of expert panel discussions, a focus group, interviews, and an online survey, was used. In initial testing, participants completed the PROM daily for 14 days via a smartphone application. This study was performed from March 14, 2022, December 12, 2023. The CF community were involved throughout the development via a focus group (n=7 pwCF), interviews (n=11 pwCF), and an online survey (n=180 pwCF). A formative model was confirmed for the PROM. The final PROM, CF Tummy Tracker, consists of 10 items capturing gastrointestinal symptom burden, tested in 151 pwCF. The PROM reported no floor or ceiling effects, high test-retest reliability (intra-class correlation coefficient=0.94), and strong correlation with the anchor question. CF Tummy Tracker aims to address the gap in validated CF-specific PROMs for daily completion. Further testing of the psychometric properties of the PROM are planned in a new patient cohort to validate its use in clinical trials and support its use in both electronic and paper formats to increase accessibility.