Accuracy of a Rapid Antigen Test Kit for Identifying Covid-19 infected Patients in the Emergency Department of Somdejphrajaotaksin Maharaj Hospital, Tak Province

Abstract

Due to a significant serge of COVID-19 in communities and workplaces, the use of antigen test kits (ATK) to identify COVID-19 patients was therefore initiated in Thailand. This observational analytical study aimed to assess the performance of using ATK to identify SARS-CoV-2 infections in ED patients with and without symptoms, as compared to the gold standard reverse transcription polymerase chain reaction (RT-PCR). The study was conducted using data compiled from the hospital’s electronic database of outpatient medical records. Sensitivity and specificity of the ATK were calculated overall and also according to the patient symptoms. Assay sensitivity was assessed according to the cycle threshold (Ct) values. From September 1^st, to October 31^st, 2021, there were 382 ED patients screened by using both ATK and RT-PCR through nasopharyngeal swab. The ATK’s sensitivity was detected at 72.22% (95%CI=46.52-90.31) while the specificity was 99.18% (95%CI=97.61-99.83). The values of sensitivity and specificity in detecting SARS-CoV-2 using ATK in symptomatic versus asymptomatic patients were similar. The ATK’s sensitivity value rose to 100% when Ct values were less than or equal to 20 and fell to 20.00-33.33% when Ct values were greater than 30. In conclusion, the use of ATK benefited a COVID-19 screening among ED patients as it yielded high specificity values, making immediate isolation of COVID-19 infected patients possible. The limitation of using this ATK was found when patients had low viral loads in the upper respiratory tract (or patients with a high Ct values). The ATK might not be able to sufficiently identify SARs-CoV-2 infection in this group of patients.