Covid testing

Updated: Jan 25

PCR vs Rapid test

Written by Dr Veronica Neumann

PCR testing

· Specificity >97%, sensitivity 98% in symptomatic patients 1

· Specificity >99%, sensitivity 81-90% in asymptomatic patients 2

· Amplifies genes so a small amount of coronavirus can be detected 1

· Gold standard 3

Rapid testing

· Specificity 99.2%, sensitivity 91% in symptomatic patients 3

· Specificity 98-100%, sensitivity 36-82% in asymptomatic patients 4

· Faster but less accurate than PCR 5

· Lab-made antibodies search for antigen made by virus 5

· No amplification- there must be enough viral antigen in sample to get positive test B

o Detect infection early in the disease course (within 5 to 7 days after symptom onset) when viral loads are high 5

· In early stages of infection, not a lot of virus is in the nose and throat- making sample collection less accurate 3

· Results correlate better with patient infectiousness than PCR 5

Other things to note:

· Symptomatic people with a negative rapid test should retest if they have a high probability of infection 1

· Asymptomatic people with known COVID exposure should test 5-7 days after exposure and if rapid testing is negative, they should test again 2 days later. 1

1. Drain, P. K. (2022). Rapid Diagnostic Testing for SARS-CoV-2. New England Journal of Medicine.

2. Caliendo, A. M., & Hanson, K. E. (2022, January 13). COVID-19: Diagnosis. UpToDate. Retrieved January 20, 2022, from https://www.uptodate.com/contents/covid-19-diagnosis#H2358377675

3. Sazed, S. A., Kibria, M. G., Hossain, M. S., Zamil, M. F., Adhikary, P. C., Hossain, M. E., ... & Alam, M. S. (2021). Clinical Evaluation of a New Antigen-Based COVID-19 Rapid Diagnostic Test from Symptomatic Patients. Diagnostics 2021, 11, 2300.

4. Winkel, B., Schram, E., Gremmels, H., Debast, S., Schuurman, R., Wensing, A., ... & Hofstra, M. (2021). Screening for SARS-CoV-2 infection in asymptomatic individuals using the Panbio COVID-19 antigen rapid test (Abbott) compared with RT-PCR: a prospective cohort study. BMJ open, 11(10), e048206.

5. Zhan, Z., Li, J., & Cheng, Z. J. (2022). Rapid Antigen Test Combine with Nucleic Acid Detection: A Better Strategy for COVID-19 Screening at Points of Entry. Journal of Epidemiology and Global Health, 1-3.

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