J Korean Med Sci.  2022 May;37(21):e168. 10.3346/jkms.2022.37.e168.

Positivity of Rapid Antigen Testing for SARS-CoV-2 With Serial Followed-up Nasopharyngeal Swabs in Hospitalized Patients due to COVID-19

  • 1Department of Laboratory Medicine, Chung-Ang University College of Medicine, Seoul, Korea
  • 2Department of Pulmonary Medicine, Hyundae General Hospital, Chung-Ang University, Namyangju, Korea
  • 3Department of Orthopaedic Surgery, Chung-Ang University Hospital, Seoul, Korea
  • 4Department of Orthopaedic Surgery, Hyundae General Hospital, Chung-Ang University, Namyangju, Korea
  • 5Department of Internal Medicine, Hyundae General Hospital, Chung-Ang University, Namyangju, Korea
  • 6Department of Pediatrics, Chung-Ang University Hospital, Seoul, Korea


Despite the accuracy of nucleic acid amplification tests (NAATs), rapid antigen tests (RATs) for severe acute respiratory syndrome coronavirus-2 are widely used as point-of-care tests. A total of 282 pairs of reverse transcription-polymerase chain reaction and Standard Q COVID-19 Ag tests were serially conducted for 68 patients every 3–4 days until their discharge. Through a field evaluation of RATs using direct nasopharyngeal swabs, the sensitivities were 84.6% and 87.3% for E and RNA-dependent RNA polymerase (RdRp) genes, respectively, for specimens with cycle thresholds (Cts) < 25. The Ct values of E and RdRp genes for 95% detection rates by RATs were 16.9 and 18.1, respectively. The sensitivity of RAT was 48.4% after the onset of symptoms, which was not sufficient. RAT positivity gradually decreased with increased time after symptom onset and had continuously lower sensitivity than NAATs.


Antigen Test; COVID-19; Nucleic Acid Amplification Techniques; SARS-CoV-2


  • Fig. 1 Logistic regression analyses for the percentage of positive results from the Standard Q COVID-19 Ag kit according to the cycle thresholds of E (A) and RdRp (B) genes in the severe acute respiratory syndrome coronavirus-2 reverse transcriptase-polymerase chain reaction.

  • Fig. 2 (A) Positive rates of the Standard Q COVID-19 Ag kit and nuclear acid amplification tests according to the number of days after symptom onset. (B) RAT (Standard Q COVID-19 Ag kit) results of COVID-19 patients according to the number of days after symptom onset and cycle threshold values. Error bars represent 95% confidence intervals.NAAT = nucleic acid amplification test, RAT = rapid antigen test.


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