The precise diagnosis of COVID-19 is of outmost importance in order to effectively treat patients and prevent SARS-CoV-2 transmission. Herein, we evaluated the sensitivity and specificity of the COVID-19 Antigen Detection Kit (Colloidal Gold-CG) compared with PCR in nasopharyngeal and nasal samples. A total of 114 positive and 244 negative nasopharyngeal specimens confirmed by PCR were used in this comparative study. When the PCR positive Cycle Threshold (Ct) value was ≤25, CG sensitivity was 100%. When the PCR positive Ct value was ≤33, CG sensitivity was 99%. When the PCR positive Ct value was ≤40, CG sensitivity was 89.47%. Regarding nasal swabs, a total of 109 positive and 250 negative specimens confirmed by PCR were used. When the PCR positive Ct value was ≤25, CG sensitivity was 100%. When the PCR positive Ct value was ≤33, CG sensitivity was 96.12%. When the PCR positive Ct value was ≤37, CG sensitivity was 91.74%. Specificity was above 99% regardless of the Ct value of PCR positivity for both nasopharyngeal and nasal specimens. Overall, the CG showed high sensitivity and specificity when the PCR Ct value was less than 33. Therefore, CG can be used for screening early in the disease course. Confirmatory PCR is essential when a false negative result is suspected.
Keywords: COVID-19; SARS-CoV-2; antigen test; clinical validation; nasal swab; nasopharyngeal swab; nucleocapsid.