Study objective: Laboratory test use varies across emergency departments (EDs), yet little is known about the effect of this variation on outcomes. The aim of this study is 2-fold: to stratify EDs into clusters based on similar test use, and to determine whether the clusters differ in patient operational outcomes among patients presenting to EDs with undifferentiated chest pain. Methods: We conducted a retrospective cohort study of 222,788 patients presenting with undifferentiated chest pain at 44 EDs across New South Wales, Australia, from January 2017 to September 2018. The operational outcomes measured in this study included ED length of stay, hospital admission, the Emergency Treatment Performance target, and 7- and 15-day all-cause and same-cause ED revisit rates. We performed a hierarchic cluster analysis to identify ED clusters and mixed-effects models to determine the association between the clusters and the operational outcomes. Results: Two ED clusters, moderate users (18 EDs) and high users (26 EDs), were identified. After adjustment for confounders, the median ED length of stay was greater by 15.7% (equivalent to 33.4 minutes) in high versus moderate users (95% confidence interval 6.62 to 25.52 minutes), and high users were less likely to achieve the Emergency Treatment Performance target versus moderate users (odds ratio 0.66; 95% confidence interval 0.50 to 0.86). There were no significant differences between the users in hospital admission and ED revisit rates. Conclusion: Our findings suggest that reducing test use may reduce ED length of stay and improve the chance of achieving the Emergency Treatment Performance target.