[Evaluation of a Visually-Read Rapid Antigen Test Kit (SGA V-Chek) for Detection of SARS-CoV-2 Virus]

Although the reverse transcriptase polymerase chain reaction (RT-PCR) method has been accepted as the reference method in the detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) RNA, it requires special laboratory conditions, complicated and expensive laboratory instruments, competent laboratory staff and long testing duration. Antigen testing methods such as enzyme immunoassay, fluorescent antibody and visually-read immunochromatographic rapid antigen detection (RAD) tests eliminated the above mentioned disadvantages of the RT-PCR. The aim of this study was to determine the performance of a RAD test kit (V-Chek, SGA Ltd, Ankara, Turkey). Two paired nasopharyngeal swabs were collected from each patient, and one of them was used for the RAD test, while the other one (different swab) was used to perform the RT-PCR test. SARS CoV-2 Double Gene RT-PCR kit (Bioeksen, Turkey) was used for RNA amplification on the Light Cycler 480 plate-based RT-PCR instrument (Roche, Switzerland). The SARS-CoV-2 double gene RT-PCR kit targeting the SARS-CoV-2 specific N (nucleocapsid) and Orf1ab gene regions was used for RNA amplification. The human RNaseP gene was used for nucleic acid extraction and inhibition control. The shape of the growth curves was examined and the non-sigmoidal curves were recorded as "negative". Sigmoidal curves with cycle threshold (Ct) <38 were evaluated as "positive". The Ct values of all positive results were recorded. V-Chek RAD test kit uses a colloidal gold enhanced double antibody sandwich type antigen test kit. A SARS-CoV-2 positive specimen produces a distinct color band in the test region, formed by the specific antibody-antigen colored conjugate complex. A positive or negative result is indicated by a colored line appearance on the test region. A colored line appears in the control region, independent of the SARS-CoV-2 presence. The result is visually read 10 minutes after the last drop of the sample liquid is dispensed into the sample well. Specificity and sensitivity values were calculated accepting the RT-PCR results as a standard. Agreement between two different techniques was assessed using Cohen's kappa score. 110 patients were enrolled in this study; 34 (30.9 %) of these patients had positive RT-PCR samples, with the mean of Ct values of 25.8 (95% CI= 24.1-27.5), median of Ct values of 26. In our study population, the overall sensitivity was 61.8% (95% CI= 45.4-78.1), and specificity was 100%. Taking RT-PCR as reference, Cohen's kappa score for the antigen test was 0.691. Fisher's exact test was p<0.001. In conclusion, the RAD kit used in the study determined to be useful for the rapid identification of COVID-19 patients. However, a negative result does not eliminate the possibility of COVID-19 infection and should be confirmed by RT-PCR and clinical findings.