BackgroundDecisions to isolate patients at risk of having coronavirus disease 2019 (COVID-19) in the emergency department (ED) must be rapid and accurate to ensure prompt treatment and maintain patient flow whilst minimising nosocomial spread. Reverse transcription polymerase chain reaction (RT-PCR) assays are too slow to achieve this, and near-patient testing is being used increasingly to facilitate triage. The ID NOW severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) assay is an isothermal nucleic acid amplification near-patient test which targets the RNA-dependent RNA-polymerase gene.AimTo assess the diagnostic performance of ID NOW as a COVID-19 triage tool for medical admissions from the ED of a large acute hospital.MethodsAll adult acute medical admissions from the ED between 31st March and 31st July 2021 with valid ID NOW and RT-PCR results were included. The diagnostic accuracy of ID NOW [sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV)] was calculated against the laboratory reference standard. Discrepant results were explored further using cycle threshold values and clinical data.FindingsTwo percent (124/6050) of medical admissions were SARS-CoV-2 positive on RT-PCR. Compared with PCR, ID NOW had sensitivity and specificity of 83.1% [95% confidence interval (CI) 75.4-88.7] and 99.5% (95% CI 99.3-99.6), respectively. PPV and NPV were 76.9% (95% CI 69.0-83.2) and 99.6% (95% CI 99.5-99.8), respectively. The median time from arrival in the ED to ID NOW result was 59 min.ConclusionID NOW provides a rapid and reliable adjunct for the safe triage of patients with COVID-19, and can work effectively when integrated into an ED triage algorithm.