COMPARISON OF A RAPID ANTIGEN DETECTION TEST WITH REAL TIME RT PCR FOR COVID 19 DIAGNOSIS: AN EXPERIENCE FROM A TERTIARY CARE HOSPITAL IN EASTERN INDIA.

Introduction: Rapid antigen detection tests (RADTs) were added to the repertoire of COVID-19 diagnostics to expand testing capacities and obtain quicker results. Thus this study aimed to evaluate the performance of the Standard Q Covid-19 Antigen Test in comparison to Real-Time RTPCR for the diagnosis of COVID-19 in a tertiary care hospital in Eastern India. Methods: Across-sectional study was conducted on 554 subjects, from whom 1108 nasopharyngeal swabs and 554 oropharyngeal swabs were collected. The samples were tested using the Standard Q Covid-19 Antigen Test and Real-Time RT-PCR. The sensitivity, specicity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of the rapid antigen test were calculated, considering Real-Time RT-PCR as the reference standard. Results: The sensitivity and specicity of the rapid antigen test were 33.62% and 99.77%, respectively. The PPV and NPV were 97.44% and 85.44%, respectively. The diagnostic accuracy was 86.28%, with a moderate agreement (Cohen's Kappa value = 0.442) between the two tests. The median Ct values of PCRpositive but rapid antigen-negative samples were higher than those of PCR-positive and rapid antigen-positive samples, indicating that the rapid antigen test detects samples with high viral loads. Conclusions: The rapid antigen test demonstrated low sensitivity but high specicity. It cannot be used as a standalone test for detection in symptomatic patients and must be supplemented by PCR. However, it can be used to rule out further infection in convalescing patients and contact tracing strategies. The clinical usefulness of the kit among patients with Ct values > 32 is doubtful, as there is a higher probability of false-negative results.