Concordance between two rapid diagnostic tests for the detection of antibodies against SARS-CoV-2

OBJECTIVE: To assess the agreement between two rapid detection tests (RDT) for antibodies against SARS-CoV-2 infection. MATERIALS AND METHODS: This was a cross-sectional study that used a random sample of non-hospitalized patients from the primary care management division of the Healthcare Area of Leon (58 RT-PCR-positive cases and 52 RT-PCR-negative cases). Information regarding symptoms was collected and all patients were simultaneously tested using two RDTs (Combined - cRDT and Differentiated - dRDT). The results of both tests were evaluated using the chi-square test and, for degree of agreement, the kappa coefficient. RESULTS: About 52% of the participants were women (mean age: 48.2 ± 11.0 years). A total of 58.2% were positive for d-RDT and 41.2% were positive for c-RDT. In the subjects who were RT-PCR-positive, d-RDT was positive in 72.4% and c-RDT in 55.2%; in those who were RT-PCR-negative, the percentages were 42.3% and 26.9%, respectively. The kappa coefficient observed between the two RDTs was 0.644, and was higher in patients without a fever or anosmia (0.725) and lower in those with a fever or anosmia (0.524). CONCLUSIONS: There is good agreement between the tests used in this study. Given the sensitivity observed, they can be very useful as a complement to RT-PCR.