Antibody tests for COVID-19 have been available for months, but there has been a lot of confusion among people about the benefit of getting the test done and how they are different from other tests. Here we have tried to answer some of the basic questions related to antibody tests that can help to resolve your conundrum.
What is an antibody test?
Antibody tests are used to determine if you have been infected by the SARS-CoV-2 in the past, while the RT-PCR and rapid antigen tests help to determine if you are currently infected by the virus. Also known as a serology test, an antibody test is carried out to look for antibodies. Our body produces these antibodies while fighting an infection. This is how we develop immunity against the particular bacteria or virus after being infected with them or after getting the vaccination. Antibody tests help to learn if the immune system has responded to the infection.
What is an antibody?
Whenever any disease-causing foreign pathogen enters our body, our immune system produces defensive proteins to fight them called antibodies. These antibodies are matched exactly to that organism and recognise the invader with the help of proteins on its surface called antigens.
Antigens help the antibody to target the intruder. They either kill it directly or lock it onto its antigens which is later neutralised by other immune cells. COVID-19 antibody tests help to know about the presence of the antibodies developed after being infected with the SARS-CoV-2 virus.
Our body produces different kinds of antibodies when they come in contact with the virus. These are also known as an immunoglobulin (Ig). The two major kinds are:
Immunoglobulin M (IgM): This is the first antibody our internal system produces after coming in contact with any diseases causing pathogens.
Immunoglobulin G (IgG): IgM antibodies are produced later by the immune system and play a role in creating memory cells that remain in the body to fight the virus in case of reinfection.
How does this test work?
The COVID-19 antibody test screens for antibodies or protein in your blood developed after a past encounter with the virus. Antibodies are also present in saliva, but the saliva test is not that effective.
To carry out the test, the lab technician takes a bit of your blood, which is tested to look for one or both kinds of antibodies to coronavirus- the IgM antibodies, which happen early in an infection and the IgG antibodies, which show up later
Most people develop IgG antibodies about 14 days after the onset of the first symptoms and they usually stay in your blood long after the recovery.
When to get the test done?
A COVID-19 antibody test is not used to diagnose an active infection. So, taking the test on the onset of the symptoms would not be beneficial for you. It takes time for our immune system to develop antibodies after coming in contact with the virus and only when they are present in ample amount in the blood, they can be detected in the test. It takes about 10-15 days for our immune system to develop detectable levels of IgG antibodies after exposure. IgM antibodies can be detected after four to five days.
Testing too early increases the chance of getting a false negative test, which means you may have been infected even if the test does not confirm it.
IgG antibodies can be detected in blood for several months after you have recovered from COVID-19. They can be found in the blood after mild or severe infection, asymptomatic infection and vaccination.
What is the antibody test used for?
Not everyone who gets infected with coronavirus has symptoms. As per the expert, this test can give a clear picture of how common the virus is. It can help you determine if the shot of the vaccine was effective or needs to be repeated. Also, if you think that you might have been infected with the virus or have fully recovered you can take this test to know the level of antibodies in the blood.