Background: Appendicitis is one of the most common pathologies encountered by general and acute care surgeons. The current literature is inconsistent, as it is fraught with outcome heterogeneity, especially in the area of nonoperative management. We sought to develop a core outcome set (COS) for future appendicitis studies to facilitate outcome standardization and future data pooling.

Methods: A modified Delphi study was conducted after identification of content experts in the field of appendicitis using both the Eastern Association for the Surgery of Trauma (EAST) landmark appendicitis papers and consensus from the EAST ad hoc COS taskforce on appendicitis. The study incorporated 3 rounds. Round 1 utilized free text outcome suggestions, then in rounds 2 and 3 the suggests were scored using a Likert scale of 1-9 with 1-3 denoting a less important outcome, 4-6 denoting an important but non-critical outcome, and 7-9 denoting a critically important outcome. Core outcome status consensus was defined a priori as >70% of scores 7-9 and < 15% of scores 1-3.

Results: Seventeen panelists initially agreed to participate in the study with 16 completing the process (94%). Thirty-two unique potential outcomes were initially suggested in Round 1 and 10 (31%) met consensus with one outcome meeting exclusion at the end of Round 2. At completion of Round 3 a total of 17 (53%) outcomes achieved COS consensus.

Conclusions: An international panel of 16 appendicitis experts achieved consensus on 17 core outcomes that should be incorporated into future appendicitis studies as a minimum set of standardized outcomes to help frame future cohort-based studies on appendicitis.

Level of evidence: V, Diagnostic test or criteria.