SENSITIVITY OF SARS-CoV-2 ANTIGEN RAPID DIAGNOSTIC TEST (Ag-RDT) BASED ON CYCLE THRESHOLD (Ct) VALUE

Abstract

 Rapid diagnostic test is an examination used to screen for COVID-19 disease. The analysis principle is immunochromatography, which detects SARS-CoV-2 antigens found in clinical specimens from the respiratory tract (nasopharynx and oropharynx). Evidence shows that using antigen rapid diagnostic tests (Ag-RDT) often gives false negative results; this is identified after a confirmation test using the real-time PCR gold standard. Despite being the gold standard, not all clinical laboratories have those facilities. Therefore, Ag-RDT remains an option. This study aims to determine the sensitivity of Ag-RDT based on the cycle threshold (Ct) value. This research is a diagnostic test with output in the form of sensitivity values. We used 200 clinical specimens at the Laboratorium Kesehatan Daerah (Labkesda) Depok West Java in January-June 2022. The results of the examination are arranged in cross-tabulations to be able to calculate the diagnostic value. The specificity of the Ag-RDT test was 98%, while the sensitivity was calculated based on the Ct value groups ≤25, 26-30, 31-35, and ≥35, which were 85.7%, 56%, 25.9%, and 15%, respectively. Ag-RDT has good specificity, but its sensitivity depends on the Ct value, which describes the viral load in the specimen. Nevertheless, Ag-RDT can still be used as a screening tool for COVID-19 disease, especially in areas with limited access to real-time PCR examination. However, a negative Ag-RDT result does not guarantee that not infected by SARS-CoV-2. Therefore, self-awareness is still needed to apply 6M to break the chain of SARS-CoV-2 transmission.