Accuracy and Usability of Emergency Department Diagnostic Codes: A Multicentre Observational Study.

Objectives: To evaluate the accuracy and usability of emergency department (ED) clinician-assigned diagnostic codes across all four Tasmanian public hospitals. Methods: We conducted a retrospective study of 300 ED presentations from all four public EDs in Tasmania. Two reviewers, a specialist emergency physician and a clinical research fellow, classified the accuracy of diagnostic codes across five levels which were then further classified into usable (levels 1-2) and unusable (levels 3-5). Rater agreement was evaluated. For accuracy and usability evaluation, conflicting reviewer classifications were removed. Associations between usability and patient, presentation, and site characteristics were evaluated using chi-square and Fisher's exact tests. Results: Overall rater agreement was moderate for both accuracy (69.3%, κ = 0.52) and usability (81.7%, κ = 0.58). Among 208 eligible presentations, 139 (66.8%) diagnostic codes were correct, 153 (73.6%) were acceptable for secondary use, 9 (4.3%) were clearly incorrect and 13 (6.3%) had insufficient documentation. Coding performance varied across hospitals, acuity, arrival mode, and representation intervals, with hospital-level usability ranging from 63.6% to 88.9%. Conclusions: Across all four Tasmanian public EDs, 66.8% of diagnostic codes were accurate, 73.6% were appropriate for secondary use, and 4.3% were clearly incorrect, with moderate rater agreement for accuracy and usability (κ = 0.52 and κ = 0.58). These findings, together with marked between-hospital variation, underscore the context dependence and subjectivity of ED diagnostic coding. They support a cautious approach to using ED diagnostic codes for health service planning, performance reporting, and observational research, while highlighting the need to address barriers and opportunities to strengthen coding performance.