EVALUATION OF RAPID ANTIGEN TEST PERFORMANCE WITH CLINICAL REFERENCE STANDARD rRT-PCR TEST IN SYMPTOMATIC COVID-19 PATIENTS AT A TERTIARY CARE HOSPITAL, HYDERABAD.

Dr. Shaik Sumayyah Banu, Dr. L. Prashanthi*and Dr. G. Jyothilakshmi

ABSTRACT

Background: Covid-19 pandemic emerged as a major public health emergency affecting healthcare services all over the world. Many manufacturers have developed different diagnostic kits for early diagnosis and treatment. But there is paucity of performance data on different diagnostic tests hence there is need for evaluation of rapid antigen test (RAT) performance with the clinical reference standard real-time reverse transcription-polymerase chain reaction (rRT-PCR) test. Methods: The Standard Q Covid-19 antigen test kit (SD Biosensor, Inc., Gurugram) performance was compared with the real-time RT-PCR test kit (ICMR-NIV 2019-nCoV Assay) for detection of SARS-CoV-2. The nasopharyngeal specimens from 1255 symptomatic suspected Covid-19 patients attending Osmania General Hospital, Hyderabad during Sept 2020--Feb 2021 were subjected for both the diagnostic tests. Results: Out of 1255 cases, 285 (22.7%) were positive, and 970 (77.2%) were negative for SARS-CoV-2. Out of 285 positive cases, 68 (23.8%) were rapid antigen test positive. The overall sensitivity of RAT was 23.8% and specificity was 100%. The sensitivity of RAT decreased as the duration of symptoms on testing date increased and specificity remained constant. Comparatively good sensitivity (67.9%) was seen when subjected to RAT in less than 3 days of duration of illness. Conclusions: To conclude, rapid antigen test sensitivity decreased with the increase in duration of illness and true positives reflected mean cycle threshold value of <20 whereas false negatives showed mean cycle threshold >25 on rRT-PCR test indicating that the variation in viral load reflects the rapid antigen test sensitivity.

Keywords: COVID-19, SARS-CoV-2, Rapid antigen test, rRT-PCR, cycle threshold value.