AbstractObjectivesTo evaluate the National Early Warning Score (NEWS2), currently recommended in the UK for risk-stratification of severe COVID-19 outcomes, and subsequently identify and validate a minimal set of common parameters taken at hospital admission that improve the score.DesignRetrospective observational cohort with internal and multi-hospital external validation.SettingSecondary care.InterventionsNot applicable.ParticipantsMain outcome measuresResultsTraining and temporal external validation cohorts comprised 1464 patients admitted to King’s College Hospital NHS Foundation Trust (KCH) with COVID-19 disease from 1st March to 30th April 2020. External validation cohorts included 3869 patients from two UK NHS Trusts (Guys and St Thomas’ Hospitals, GSTT and University Hospitals Southampton, UHS) and two hospitals in Wuhan, China (Wuhan Sixth Hospital and Taikang Tongji Hospital).The primary outcome was patient status at 14 days after symptom onset categorised as severe disease (transferred to intensive care unit or death). Age, physiological measures, blood biomarkers, sex, ethnicity and comorbidities (hypertension, diabetes, cardiovascular, respiratory and kidney diseases) were included.ConclusionsNEWS2 score on admission was a weak predictor of severe COVID-19 infection (AUC = 0.628). Adding age and common blood tests (CRP, neutrophil count, estimated GFR and albumin) provided substantial improvements to a risk stratification model, particularly in relation to sensitivity, but performance was only moderate (AUC = 0.753). Improvement over NEWS2 remained robust and generalisable in GSTT (AUC = 0.817), UHS (AUC = 0.835) and Wuhan hospitals (AUC = 0.918).Adding age and a minimal set of blood parameters to NEWS2 improves the detection of patients likely to develop severe COVID-19 outcomes. This finding was replicated across NHS and non-UK hospitals. Adding a few common parameters to a pre-existing acuity score allows rapid and easy implementation of this risk-scoring system.Key MessagesThe National Early Warning Score (NEWS2), currently recommended for severe COVID-19 disease in the UK shows overall poor discrimination for severe outcomes (transfer to ICU or death). It can be improved by the addition of a small number of blood and physiological parameters routinely measured at hospital admission.The addition of age and a minimal set of common blood tests (C-reactive protein, neutrophil count, estimated GFR and albumin) provided substantial improvements in a risk stratification model.Although predictive performance varied from hospital to hospital, the improvement over NEWS2 alone was consistent across different patient cohorts.The proposed addition of a limited number of dichotomised parameters is easily derived from a pre-existing acuity score would be substantially easier to implement in a short-time scale compared to novel high-dimensional risk-scoring systems.