COVID-19 Tests FAQ
COVID-19
Several testing methods have been developed to diagnose the disease. They are known as Diagnostic tests which include the Molecular, and Antigen and the non-Diagnostic Serology Antibody tests. Each have their distinct level of what they are testing, reliability, methods of use, testing equipment, results times, and required samples such as, blood, nasal-pharyngeal, nasal or oral/saliva.
No. There are two categories of COVID-19 tests: diagnostic tests, which help determine if you are infected with COVID-19, and antibody tests, which detect if you have an immune response (presence of antibodies) because of past exposure to the virus through infection or vaccination.
Diagnostic Tests
Molecular Tests
Molecular tests work by looking for the virus' genetic material in a sample from a person. This sample is then usually analyzed in a lab. For some tests, the sample can be analyzed at the point-of-care, such as at a doctor’s office.
Antigen Tests
Antigen tests are another type of diagnostic test that see if there are viral proteins in a sample taken from inside your nose with a swab. These tests are often simpler and may provide results quicker than many molecular tests, sometimes within minutes in a doctor’s office.
Antibody Tests
Antibodies are a key part of the immune system – the body’s natural defence system. They help protect us from harmful substances (pathogens) such as viruses, bacteria and other foreign invaders that would otherwise cause us harm or disease.
Antibodies are produced by your body when you’re infected by a virus and help your immune system fight off the infection. If an antibody test finds antibodies in the blood or saliva, it likely means the person has been previously infected with the virus.
An antibody (Ab), also known as an immunoglobulin (Ig),[1] is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. The immune system detects proteins (antigens) on the surface of all of our cells.
When our body is exposed to a pathogen for the first time, the immune system won’t recognise the new antigen on its surface and our body will launch an immune response. This involves producing antibodies that circulate in your blood and lock onto that specific foreign antigen to mark the cells as a problem to be eradicated.
An antibody test, sometimes called a serology test, are used detect the presence of antibodies, which are proteins made in response to infections. Antibodies are detected in the blood or saliva of people who are tested after infection; they show the body’s efforts to fight off a specific infection.
Because immunoglobulins are matched to a specific pathogen, they can be used to diagnose some diseases based on their unique structure. Antibody tests are used to detect disease-specific antibodies in a blood sample.
Antibody tests are available to diagnose (or help diagnose) a wide variety of infectious and autoimmune diseases,
Antibody tests do not detect the actual pathogens that cause an infection—they detect the antibodies that are produced in response to the infection. A positive result means "yes," the test has detected the antibody or antigen. A negative result means "no," while borderline results are considered inconclusive.
Antibodies are also known as immunoglobulins (Ig). Immuno describes immunity and globulin describes protein.2
They are produced by B cells, a specific type of white blood cell (WBC) that originates in the bone marrow.
There are 5 main types of antibodies, each with their own role to play.
Immunoglobulin G (IgG)
Immunoglobulin G (IgG) accounts for around 75% of all antibodies in the human body. Depending on the antigen, IgG can either tag a pathogen so other immune cells and proteins will recognize it, or it can promote the release of toxins to directly destroy the microorganism.
Immunoglobulin A (IgA)
Immunoglobulin A (IgA) is primarily found in mucosal tissues, such as those in the mouth, vagina, and intestines, as well as in saliva, tears, and breast milk. It accounts for 15% of all antibodies in the human body and is produced by B cells and secreted from the lamina propria, a thin layer within mucosal tissues.
Immunoglobulin M (IgM)
Immunoglobulin M (IgM) is also one of the first antibodies recruited by the immune system to fight infection. IgM populations rise very quickly when the body is first confronted with an infectious organism, and then they plummet as IgG antibodies take over. IgM is also produced by B cells and, when bound to a pathogen, will spur other antibodies and immune cells into action.
Immunoglobulin E (IgE)
Immunoglobulin E (IgE) is the antibody responsible for the allergic response that is mostly found in the lungs, skin, and mucosal membranes. IgE is produced by B cells secreted by lymph nodes or other lymphoid tissues situated near the site of the allergen (a harmless substance that induces an allergic response).
Immunoglobulin D (IgD)
Immunoglobulin D (IgD) is important in the early stages of the immune response. Unlike other antibodies, it does not actively circulate but instead binds to B cells to instigate the immune response. As a signaling antibody, IgD helps incite the release of front-line IgM to fight disease and infection.
Depending on the disease, it may take time for enough antibodies to be produced to reach detectable levels. If it's done too soon, during the early window period, the test may deliver a false negative result.
Because it takes time for the immune system to develop the COVID-19 specific antibodies, the antibody test can’t be done too early. Studies tell us that over 90% of people who have had COVID-19 will have produced the IgG antibody 14 days from the start of the illness.
So the best time to take the COVID-19 antibody test is 14–21 days after you first become unwell. How long the COVID-19 specific antibodies will continue to be detected in the blood isn’t yet fully known because the virus hasn’t been around for long enough.
Some of these antibodies will stay in circulation afterwards, so that if you’re exposed to the same pathogen again, the immune system can quickly redeploy the antibodies and destroy the pathogen without us becoming unwell. This is immunity. Sometimes the immune system can’t retain enough of these antibodies, or any at all, so we are at risk of reinfection.