Diagnostic Accuracy of STANDARD Q COVID-19 Antigen Detection Kit in Comparison with RT-PCR Assay using Nasopharyngeal Samples in India

Introduction: Real-time Reverse Transcription-Polymerase Chain Reaction (RT-PCR) can be considered to be the gold standard for diagnosis of Coronavirus Disease-2019 (COVID-19). Though it is highly accurate but has some limitations in terms of its use, which means that Rapid Antigen Tests (RAT) can support COVID-19 mitigation efforts.

Aim: To estimate sensitivity, specificity and degree of agreement of STANDARD Q COVID-19 Antigen Detection Kit in comparison to real-time quantitative RT-PCR (qRT-PCR).

Materials and Methods: This cross-sectional study was conducted at Government Medical College, Srinagar, Jammu and Kashmir, India, in April 2021. Socio-demographic and clinical information was collected on a pretested schedule after which two consecutive nasopharyngeal swabs were collected from each subject. One sample was tested using the STANDARD Q COVID-19 antigen test and the other was tested using qRT-PCR. Sensitivity and specificity were calculated using standard formulas. Cohen’s Kappa was calculated and Mann-Whitney U test was used for comparison.

Results: The study included 473 subjects with a mean age of 38.4±12.2 years. Around 1/4th (124 subjects) of subjects were symptomatic at testing with the most common symptoms being fever (57.2%), cough (50%), sore throat (43%), myalgia (25%) and diarrhoea (13%). The sensitivity, specificity, positive likelihood ratio and negative likelihood ratio were estimated to be 54.4%, 99.2%, 71.49 and 0.46, respectively. The Cohen’s Kappa between the two tests was 0.644. Cycle threshold value was significantly lower in subjects with symptoms and those with a positive rapid test among those positive on qRT-PCR.

Conclusion: The STANDARD Q COVID-19 antigen test has a reasonable sensitivity, high specificity with a substantial inter-test agreement in comparison to qRT-PCR.