Objective Early warning scores (EWS) are used to predict patient outcomes. We aimed to determine which of 13 EWS, based largely on emergency department (ED) vital sign data, best predict important clinical outcomes.

Method We undertook a prospective cohort study in a metropolitan, tertiary-referral ED in Melbourne, Australia (February–April 2018). Patient demographics, vital signs and management data were collected while the patients were in the ED and EWS were calculated using each EWS criteria. Outcome data were extracted from the medical record (2-day, 7-day and 28-day inhospital mortality, clinical deterioration within 2 days, intensive care unit (ICU) admission within 2 days, admission to hospital). Area under the receiver operator characteristic (AUROC; 95% CIs) curves were used to evaluate the predictive ability of each EWS for each outcome.

Results Of 1730 patients enrolled, 690 patients were admitted to the study hospital. Most EWS were good or excellent predictors of 2-day mortality. When considering the point estimates, the VitalPac EWS was the most strongly predictive (AUROC: 0.96; 95% CI: 0.92 to 0.99). However, when considering the 95% CIs, there was no significant difference between the highest performing EWS. The predictive ability for 7-day and 28-day mortality was generally less. No EWS was a good predictor for clinical deterioration (AUROC range: 0.54–0.70), ICU admission (range: 0.51–0.72) or admission to hospital (range: 0.51–0.68).

Conclusion Several EWS have excellent predictive ability for 2-day mortality and have the potential to risk stratify patients in ED. No EWS adequately predicted clinical deterioration, admission to either ICU or the hospital.