Detection of Antibodies (Serology)

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Testing to see who has had COVID-19 could help governments and individuals, however looking for the presence of antibodies in the blood is difficult and these antibody tests need a high degree of accuracy. Part of the response of the immune system is the production of antibodies including IgM and IgG.  The IgM antibodies are the first to be generated by the body after the infection. Then the IgG antibodies are produced later and replace the IgM and it is these antibodies that stay in the blood for many years. 

The majority of the current antibody tests target the spike protein which is the sole protein on the viral surface responsible for entry into the host cell, and so the main part of the virus that gets an antibody response. However, the amino acid structure of the spike protein has a very large overlap with the four seasonal coronaviruses that circulate in humans. Targeting the wrong site on this protein means an antibody test is unable to distinguish between people who have had COVID-19 and those who have had the common cold.

 

The tests have to be:

  • Specific​

    • The test needs to correctly identify the person as not having had the virus i.e can tell that they do not have the antibodies. This is important if the test gave a false positive somebody might think that they have had the virus when they have not. 

  • Sensitive

    • This means that the test picks up all those who do have antibodies. The higher the sensitivity the better the test . A false negative means that it says somebody doesn't have antibodies when they do

There are two types of test:

1. ELISA (enzyme-linked immunosorbent assay)

The blood samples are sent to a laboratory to be tested and could take a few hours. However as many people have been exposed to the common cold corona viruses and will therefore have antibodies for this, the test needs to be able to distinguish between them. 

 

Recently two companies Roche and Quotient said that they have US and EU approval for an antibody test with 100% sensitivity and 99.8% specificity – however both these tests require a blood sample taken under medical supervision that must be analysed in a lab.  Another company Abbott has also had approval for a similar test where a testing kit is sent home, blood taken by pricking a finger and the resulting blood sample sent to a lab for testing. 

2. LIFA (Lateral Flow Assay) home test

This test can be done at home by pricking a finger and putting the blood on a strip of paper similar to a pregnancy test where a line appears on the test within minutes showing whether you have antibodies or not. It would be suitable for mass distribution and would be relatively inexpensive but the results are currently not accurate enough to get government approval in the UK.