Performance Characteristics and Utility of the Standard Q COVID-19 Antigen Test for Emergency Admissions to Healthcare Facilities

This study evaluated the performance of the COVID-19 Ag-RDT compared to the real-time reverse transcription-polymerase chain reaction (rtRT-PCR) for SARS-CoV-2 detection and its use among patients referred for emergency admission. A total of 120 nasopharyngeal swabs were collected from patients referred for emergency admission and immediately preceded for testing to the Unit of Clinical Microbiology. Out of 60 Ag positive tests, 53 (88.3%) were confirmed by rtRT-PCR, while 7 (11.7%) tested negative (false positives). Out of 60 Ag negative tests, 56 (93.3%) were confirmed negative by rtRT-PCR, and 4 (6.7%) were positive (false negatives). Ct value comparison was performed for 53 samples that were positive by both methods: 8 (15.1%) isolates had Ct value up to 20; 37 (69.8%) 21 to 30 and 8 (15.1%) 31 to 40, respectively. The sensitivity of the analyzed rapid Ag test was 92.9%, and specificity 88.9%. The accuracy of the Ag test was 90.8%. This study has shown that rapid Ag tests can be used in emergency admissions to healthcare facilities. However, rtRT-PCR should be considered after negative antigen test results in symptomatic patients, and after positive antigen test results in asymptomatic persons.