What is the COVID19 antibody test?

Antibody Tests Tebu Bio

For over two years now, COVID-19 infection has changed our lives and keeps doing it day after day. Through time, we have learnt how to preserve our communities as much as possible from its spread.

COVID-19 vaccines are meant to protect individuals against the development of this infectious disease, which can be potentially severe, to limit the severe cases of the illness and to protect the organism of an infected individual. Even if these vaccines have been introduced to the world’s population, it is not 100% guaranteed that individuals won’t be contaminated or sick. And even if vaccines and tests are now available for everyone, scientists are still looking for efficient ways to reduce the effect of this pandemic.

With the arrival of all these COVID-19 tests, one might feel quite lost regarding their use, their accuracy, etc. Thus, here are some explanations regarding COVID-19 antibody test.

Antibody test vs diagnostic test.

When you start getting infected with SARS-CoV-2, the virus that causes COVID-19 disease, the response from your immune system may not be immediate. Indeed, it is highly possible that your body has never encountered it before.

But after some time, T-cells (which are components of the immune system) can combat it and bring an immune response to the threat they are facing. When doing so, T cells interact with B cells (which are also part of the immune system). From this cell/cell interaction, B cells are going to produce antibodies which will then be able to recognise a potential future infection from that same specific virus.

Once antibodies are produced, they are meant to protect the system from a new infection with the virus or to prevent people from getting severely ill, but only for a certain period of time.

Type of test: antibody

Antibody tests are serology tests made to detect antibodies in the blood of a person who was previously infected with the virus, or people who received a dose of COVID-19 vaccine.

These antibodies are proof that the body has put efforts to eradicate the infection whether the virus has been inoculated through a vaccine shot, or the patient has been contaminated by their peers or after a contact with an infected person.

If your immune system doesn’t encounter the virus, the number of antibodies decreases. Consequently, the number of antibodies in the blood starts decreasing. The speed of the decrease depends on many factors and can be different from one person to another.

As you may have understood, the goal of using these serologic tests performed usually after a full recovery from COVID-19 is to determine if you were infected with the virus in the past and if you now have antibodies against it.

The use of antibody tests is mainly decided by local health departments in order to know the number of people who were infected with COVID-19 and who recovered from it, whether the individual had symptoms of COVID-19 or not.

Type of test: diagnostic

Diagnostic tests are quite different; they have been developed in order to determine if a patient is currently suffering from the disease. These tests can be used on patients who have symptoms in order to detect the presence of the virus at an early stage. They can also be used on people without symptoms or on people who have been in touch with infected people, to detect the presence of the virus in the cells, and thus preventing a spread of the infection.

They can be taken care of quite rapidly and their close relatives or contacts can be warned and isolated in order to help stop the spread the best possible way. Diagnosing the infection can be done with a PCR test or an antigen test. This test detects some proteins that are active within the virus.

But no COVID-19 test is 100% accurate. False negative or false positive results are always possible. This is why the Centers for Disease Control and Prevention gave some guidelines for people to keep following until the pandemic is under full control.

How do antibody tests work?

Since they were released and made accessible to the world’s population, COVID-19 antibody tests have received the utmost attention. Indeed, this type of test is done to reveal a previous infection with SARS-CoV-2. This type of test is highly appreciated by the scientific community, as the results are delivered quite rapidly and with a high level of accuracy.

The antibody test is a serology one, which is meant to detect previous infections with COVID-19. This test works like a pregnancy test, with a physical principle called capillarity; a principle that involves the flowing of liquids in narrow spaces, without needing energy. But let’s dive a bit deeper and see how it works.

First a sample of blood is taken from a patient, who has supposedly been infected with COVID-19. This sample is then placed at one end of a strip which contains a pad that is going to soak up the blood. The liquid then spreads from one end of the strip to the other. Next to where the blood was placed, there is a conjugate pad which contains pieces of SARS-CoV-2 viral “S” protein with colour probes, to help the detection of antibodies.

If the patient has developed antibodies to fight SARS-CoV-2 in the past, specific antibodies will attach to the colour probes that are linked to this protein. These colour probes attached to the viral “S” protein are going to allow the detection of the specific antibodies related to SARS-CoV-2. The capillarity principle starts, and the blood sample moves on to the next part of the strip, designed to detect SARS-CoV-2 IgM antibodies.

If the patient’s sample contains any of these IgM antibodies, they will be stopped in this region of the strip and the colour attached to the viral “S” protein will form a coloured line. Then the sample keeps moving, to the next part of the strip where it contains IgG antibodies. The detection of these antibodies works the same way it does for IgM ones.

At the very end of the strip, a control row is displayed, to make sure the capillarity principle worked perfectly. This line will be coloured only if the blood sample has made its way through the entire strip. IgM and IgG antibodies are the two antibodies we are going to look for if we want to say if a patient has been infected or not.

The results of this antibody test can be read within a couple minutes. If one of the antibody lines, or the two of them appear in colour and the control line is coloured as well, it means that the patient has previously been infected with COVID-19.

Antibody tests are a good way to determine if people were infected with the virus, but scientists are now trying to know more about immunity after recovering from the infection, and understand how long antibodies remain in blood cells.


–    Centers for Disease Controls and Prevention. “Using Antibody Tests for COVID-19.” Published on September 10, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests.html


–    Mayo Clinic. “How do COVID-19 antibody tests differ from diagnostic tests?” Answers provided by William F. Marshall. III M.D. Mayo Clinic, December 10, 2020. https://www.mayoclinic.org/diseases-conditions/coronavirus/expert-answers/covid-antibody-tests/faq-20484429 


–     Research America. “Explained: How a COVID-19 serology test works and obstacles to its use.” Sarah Ackerman, PhD and Mark Von Eisenburg, MS. May 19, 2020.



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