The optimal threshold for prompt clinical review: An external validation study of the national early warning score

Aims and objectives The aim of this study was to determine the optimal threshold for national early warning score in clinical practice. Background The national early warning score is an aggregate early warning score aiming to predict patient mortality. Studies validating national early warning score did not use standardised patient outcomes or did not always include clinical workload in their results. Since all patients with a positive national early warning score require a clinical workup, it is crucial to determine the optimal threshold to limit false‐positive alerts. Design An external validation study using retrospectively collected data of patient admissions in six Belgian hospitals. Methods We adhered to the STARD guideline for reporting. Two sample groups were selected: the cross‐sectional sample (admitted patients, 1 day every 4 months) and the serious adverse event sample (all patients with unexpected death, cardiac arrest and unplanned admission to the intensive care unit). The maximum registered national early warning score value was collected in both groups. Predictive values were used as estimates for clinical workload. Results We collected 1,523 in the cross‐sectional sample and 390 patients in the serious adverse event sample. A national early warning score ≥5 had a predictive value of 6.8% and a negative predictive value of 99.5% to predict unexpected death, cardiac arrest with cardiopulmonary resuscitation or unplanned admission to intensive care (AUROC 0.841). The performance of national early warning score differed between outcome measures. Considering the predictive value, the optimal threshold for national early warning score is ≥5. Conclusions We validated national early warning score to be applied in general hospital wards and confirmed the optimal threshold (≥5). Relevance to clinical practice When a patient has a national early warning score