Evaluation of Efficacy of Rapid Antigen Test against RT-PCR and its Correlation with Cycle Threshold (CT) values: an Institutional Experience

Abstract

Rapidly increasing COVID-19 or SARS-CoV-2 in whole world caused a tremendous pressure on existing diagnostic setup to give accurate diagnosis on time by gold standard RT-PCR technique forcing scientist to think beyond RT-PCR which ultimately ended with invent of Rapid antigen test which can give about 100% specific and rapid result but may miss many case due to low sensitivity. So we wanted to evaluate the Rapid antigen test against RT-PCR for its diagnostic accuracy. We followed standard procedure for sample collection, Rapid antigen test and RT-PCR test. In about one and half month span we collected 554 antigen negative samples in our hospital. About 13% sample (74/554) turned out as positive by RT-PCR test. About 40 % (30/74) positive samples had low Ct value (<25) indicating higher viral load present in those patients. Above findings indicate that only antigen test will miss a significant portion of positive cases with higher viral load which may complicate the pandemic by unknowingly spreading the virus within the society. So we should try to improve our infrastructure to carry out more RTPCR test so we can detect more cases to identify and isolate them from others to prevent or slowdown the transmission chain.