Cryptoglandular Anal Fistula Core Outcome Measurement Set (AFCOMS): standardised definitions and measurement instruments.

Background: Cryptoglandular anal fistula is a condition that significantly impairs quality of life in patients. Despite the recent development of the Anal Fistula Core Outcome Set (AFCOS), which identified ten key outcomes, variation in outcome definitions and measurement instruments hampers comparability across studies and limits evidence synthesis. An essential final step to improve future comparability is the development of a Core Outcome Measurement Set (COMS) aligned with AFCOS; this study aimed to establish such a COMS through an international, consensus-driven process. Methods: This study was conducted in three phases according to the Core Outcome Measures Effectiveness Trials (COMET) methodology. Phase 1 included a scoping review to identify definitions and measurement instruments for all AFCOS outcomes. Phase 2 involved summarising available evaluation of psychometric properties and overall feasibility of each instrument according to the COSMIN criteria. Phase 3 consisted of an international two-round Delphi survey conducted from September 2023 until May 2024 and a final consensus meeting in June 2024 with patients and healthcare professionals to agree on definitions, measurement instruments and timepoints. Findings: In Delphi round 1, 92 of 110 participants (85 health professionals, 7 patients, from 18 countries) completed the survey (84% overall response). Many instruments had insufficient content validity when evaluated by patients. In round 2, 70 of 76 participants (63 professionals, 7 patients) completed the survey (92% response). A final consensus meeting was attended by 27 participants (26 clinicians and 1 patient representative). Clinical fistula healing was defined as the absence of discharge symptoms, abscess, infection or inflammation, with no recurrence or persistence for ≥6 months. Recurrence was defined as the reappearance of symptoms after this healing period. Radiological healing was defined as complete resolution of any visible fistula tract and inflammatory mass, ± fibrosis on MRI. Development of an additional fistula was defined as a separate, anatomically distinct tract. Complications were classified according to the Clavien-Dindo system, and reinterventions were limited to surgical or radiological procedures. The Anal Fistula Quality of Life Scale was selected to assess quality of life, fistula symptoms and psychological impact, the Vaizey score to assess continence, and a numerical rating scale to assess patient satisfaction. Timepoints were set at 3- and 12-months post-treatment. Interpretation: AFCOMS provides standardised outcome definitions and measurement tools for use in future cryptoglandular anal fistula research, enhancing reporting consistency and enabling evidence synthesis. Funding: There was no external funding for this study. The study was conducted independently by the authors.