ObjectivesUsing case review to determine whether a patient experienced a delayed diagnosis is challenging. Measurement would be more accurate if case reviewers had access to multi-expert consensus on grading the likelihood of delayed diagnosis. Our objective was to use expert consensus to create a guide for objectively grading the likelihood of delayed diagnosis of appendicitis, new-onset diabetic ketoacidosis (DKA), and sepsis.MethodsCase vignettes were constructed for each condition. In each vignette, a patient has the condition and had a previous emergency department (ED) visit within 7 days. Condition-specific multi-specialty expert Delphi panels reviewed the case vignettes and graded the likelihood of a delayed diagnosis on a five-point scale. Delayed diagnosis was defined as the condition being present during the previous ED visit. Consensus was defined as ≥75% agreement. In each Delphi round, panelists were given the scores from the previous round and asked to rescore. A case scoring guide was created from the consensus scores.ResultsEighteen expert panelists participated. Consensus was achieved within three Delphi rounds for all appendicitis and sepsis vignettes. We reached consensus on 23/30 (77%) DKA vignettes. A case review guide was created from the consensus scores.ConclusionsMulti-specialty expert reviewers can agree on the likelihood of a delayed diagnosis for cases of appendicitis and sepsis, and for most cases of DKA. We created a guide that can be used by researchers and quality improvement specialists to allow for objective case review to determine when delayed diagnoses have occurred for appendicitis, DKA, and sepsis.