Comparison of various tests of Covid-19

Last Updated 15 January 2021. Cellspect Co., Ltd.

Various Covid-19 tests are being used currently. Generally speaking, there are two kinds of tests are available for COVID-19: viral tests (diagnostic tests) and antibody tests. Viral tests are to detect whether a person is currently infected, including PCR and antigen tests. Antibody tests are to detect whether a person had an infection in the past. 

 

PCR test

PCR tests detect the presence of viral RNA. PCR tests are considered the most accurate and “gold standard” for diagnosing active coronavirus infection. This test is typically highly accurate. However, the testing cost is relatively high, the evaluation time is longer, and the analysis needs professional staff and equipment.

 

Antigen test

Antigen tests detect specific proteins from SARS-CoV-2, the virus that causes Covid-19. Antigen test is not as sensitive (accurate) as the standard PCR test and may have higher false negative rate. The advantages of antigen tests are the lower cost and lower demands on the expertise of the staff. So far, many rapid antigen tests have been developed and the results may be shown very quickly (15-30 minutes). The rapid antigen test reveals patients at the peak of the infection when the body has the highest concentration of these proteins. Positive results are usually highly accurate, but increased chance of false-negative can happen. Negative results may need to be confirmed with a PCR test.

 

Antibody test (serology test)

Antibody tests measure antibodies against SARS-CoV-2 virus, detecting if the immune system has responded to the SARS-CoV-2 virus in the past. Antibodies are not present at the onset of the disease. According to the U.S. CDC, antibodies against SARS-CoV-2 virus usually start developing within 1 to 3 weeks after infection. Antibody tests generally produce results in a few minutes based on a drop of blood taken from the finger; some tests may take 1-3 days if blood is drawn for testing. In some cases, antibody tests can help determine when Covid-19 illness occurred, since we know that IgM is formed before IgG and that IgM goes away before IgG. It can also help determine who qualifies to donate convalescent plasma for Covid-19 treatment. Moreover, antibody tests could be useful in measuring the durability of vaccine responses

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A negative viral test means that person was probably not infected at the time their sample was collected. However, it doesn’t mean they won’t get sick – it only means that they didn’t have COVID-19 at the time of testing. A negative antigen test means that SARS-CoV-2 viral proteins were not detected. Due to the false-negative rate of antigen test, it is recommended to do a PCR test for confirmation.

 References:

  1. HORIZON The EU Research & Innovation Magazine: https://horizon-magazine.eu/

  2. U.S. Food and drug administration: https://www.fda.gov/

  3. World Health Organization: WHO https://www.who.int/

  4. Centers for Disease Control and Prevention: https://www.cdc.gov/

  5. Texas Health and Human servicess: https://hhs.texas.gov/

  6. Kazuo.I et al, Antibody response patterns in COVID-19 patients with different levels of disease severity—Japan, preprint, doi: https://doi.org/10.1101/2020.11.20.20231696;

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