What Is An AntibodyTest?

An antibody test is a screening procedure for something called antibodies in our blood. Our body makes these while fighting an infection, such as COVID-19. Antibodies are how you build immunity towards a virus. You may have also heard it being referred to as a serology test. The antibody test does not check for the virus itself. Instead, the main function of this test is to see whether your immune system, which is your body’s defense against illness, has responded to the infection or not.

Differences BetweenTests For COVID-19

A coronavirus test, sometimes called a diagnostic test or PCR, looks for signs of active virus. It is simpler and faster than an antibody test. But it tells you only if you have the virus in your body at the moment when you are tested. An antibody test can show if you had the virus at some point in the past, by showing you if your system has developed the antibodies particular to COVID-19.

• COVID-19 PCR (Swab) Test is not an antibody test. It uses a long swab to collect a sample, including physical pieces of coronavirus, from the back of the nasal cavity where it meets the throat (i.e.the nasopharynx). A positive result indicates or confirms the presence of the COVID infection. However, it is to be noted that this test is specifically and only for coronavirus and will not confirm or deny the presence of any other virus. A negative result indicates that the SARS-CoV2 virus that causes COVID-19 was not found. It is important to note that it is possible to have a very low level of the virus in the body with a negative test result. This testis needed to identify the presence of the SARS-CoV-2 virus that causes the COVID-19 disease, and is perhaps the most accurate form of testing to confirm presence of the virus.

• COVID-19 (Coronavirus) Antibody (Serology) Test is a blood test designed to detect antibodies (immunoglobulins, IgG and IgM) against the coronavirus that causes COVID-19. Antibodies are proteins produced by the immune system in response to an infection, and are specific to that particular infection. They are found in the liquid part of our blood,which is called serum or plasma. IgM and IgG may either be ordered together or separately.

• Antibody Test for IgG detects IgG antibodies that develop in patients within 7 to 10 days after COVID-19 symptoms surface. IgG antibodies remain in the blood after an infection has passed. These antibodies indicate that you may have had COVID-19 in the recent past and have developed antibodies that may protect you from reinfection. However, it is unclear at this point how much protection antibodies provide against reinfection.

• Antibody Test for IgM detects IgM antibodies,which are usually the first antibody produced by the immune system when a virus attacks. A positive IgM test indicates that you may have been infected and that your immune system has started responding to the virus.  When IgM is detected you may still be infected, or you may have recently recovered from a COVID-19 infection.

How Are IgM and IgG Different?

• IgM is one of the first antibodies produced during infection. Although IgM is the largest antibody by size, its relative abundance in the blood is only about 10% of total antibody count.

• IgG is the smallest and most abundant circulating antibody. It makes up approximately 80% of total antibody count and is primarily found in serum or plasma. IgG typically appears later in infection when mature cells receive signals to switch from production of IgM to IgG. IgG is a key player in establishing post-infection immunity.

Most people have IgG antibodies about 14 days after symptoms start. They usually stay in your blood long after the infection goes away, but exactly how long remains unclear.

Why Do We Need Antibody Testing?

Tests such as the antibody test are helping with experimental treatment for COVID-19 using something called convalescent plasma. Plasma is the liquid part of your blood. Scientists are studying how antibodies in plasma donated by recovered COVID-positive patients might help those who are ill with the virus, as this plasma may help sick people get better faster. However, more research is required on this matter.

If you were diagnosed with COVID-19 and are now fully recovered, you may be able to help. Your immune system may now be producing antibodies to protect you from becoming infected again with coronavirus. If so, your plasma may be rich in these antibodies and be helpful in the treatment or prevention of COVID-19 disease in others.

If you are interested in donating plasma, please fill out this form and you could help save a life.

Interpreting the Results

If you test positive for SARS-CoV-2 antibodies, it could mean you have had the virus. It is also possible to get a “false positive” if you have antibodies but contracted a different kind of coronavirus. A positive result could mean you have some immunity to the coronavirus. However, it is too early to know how strong it is or how long it might last.

A negative result means you have not come into contact with the virus, or it could mean you have not had it long enough to make antibodies. You may also have been exposed and not have antibodies. This is called a “false negative”.

Regardless of your test result, if you do not have symptoms, you do not need follow-up.However, if you are displaying symptoms, you might need to get a diagnostic test (PCR) to look for signs of active virus. As there is a chance that test results can be wrong and because there is a lack of knowledge about the virus,it is very important to keep following official safety guidelines after your test. Stay home as much as you can, wear a mask when you are in public, and wash your hands as often as you can.