Diagnostic accuracy of rapid antigen test for COVID-19 in an emergency department

•Diagnostic accuracy of Lumira Dx rapid antigen diagnostic (RAD) test is too low to be diagnostic.•RAD test can be used when pre-test probability of infection is very high.•RAD test cannot be used to rule out disease in asymptomatic patients. Use of antigen tests for the diagnosis of COVID-19 has become widespread. The aim of this study was to evaluate the diagnostic accuracy of the nasopharyngeal rapid antigen diagnostic (RAD) immunoassay LumiraDx UK in an Emergency Department (ED). All patients admitted to our ED between November 11 and December 8, 2020, and had both a RAD test and a real-time-reverse-transcription-polymerase-chain-reaction (RT-PCR) test were enrolled. RAD was considered as the index test and RT-PCR test was used as the reference standard. Sensitivity, specificity, negative and positive predictive values, and likelihood ratios were calculated with the 95% confidence interval. The sensitivity and specificity of RAD were 34.2% and 92.3%. Positive and negative likelihood ratios were 4.4 and 0.71. Our results demonstrate that the diagnostic accuracy of the LumiraDx RAD test is too low for routine use as a diagnostic method in the ED.