Comparison of RT-PCR, RT-LAMP, and antigen quantification assays for the detection of SARS-CoV-2

Tanimoto, Yoshihiko; Mori, Ai; Miyamoto, Sonoko; Ito, Erika; Arikawa, Kentaro; Iwamoto, Tomotada

A rapid and simple alternative test to real-time reverse transcription polymerase chain reaction (RT-PCR) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required to help curb the spread of this infection. In this study, we compared the RT-PCR method with the chemiluminescent enzyme immunoassay (CLEIA) and reverse transcription loop mediated isothermal amplification (RT-LAMP) methods. The results for the number of SARS-CoV-2 RNA copies and the CLEIA antigen quantification values were highly correlated. The detection limit for antigen quantification was 42.8 RNA copies for saliva samples and 23.4 copies for nasopharyngeal swab (NPS) samples. The number of RNA copies and RT-LAMP threshold time (Tt) values were inversely correlated for both purified RNA and purification-free crude RNA. RT-LAMP with purified RNA detected low copy numbers of RNA (5-50 copies) whereas fewer than 250 RNA copies could not be detected using crude RNA. CLEIA antigen quantification is potentially useful for large scale screening because it is compatible with high throughput testing. RT-LAMP with crude RNA samples is applicable to rapid point-of-care testing because it can directly use the patient specimen. It is important to select a diagnostic method that is simple and rapid compared to RT-PCR, depending on the situation.