ANTIBODY TESTS

Antibodies are formed by your body in response to something foreign entering your body. It might be a virus, like SARS-CoV-2, a bacterium, or even something like pollen. Your body recognizes this invader, also known as a pathogen, and starts to produce a defense against it. One part of this defense is antibodies. In an antibody test, scientists look to see whether you've formed any antibodies against SARS-CoV-2. If you have, it means that at some point you were infected with SARS-CoV-2. Though there is more than one way to do an antibody test, we will discuss the indirect ELISA method.

TESTING PROCESS

Thomas, Liji. “COVID-19 and Antibodies.” News Medical, www.news-medical.net/news/20200716/Children-with-MIS-C-have-different-antibody-responses-than-adults-with-COVID-19.aspx.

So how do scientists do it? First, you need to know that antibodies bind to antigens, which are a specific part of a pathogen, and that each antibody only recognizes a single antigen (check out the Types of Tests page for more info). As an example, think of how you might recognize a door in the dark. Reaching out to feel it, you might not recognize the door itself as a door, but if felt the handle, you would likely recognize it right away, letting you know that you're standing in front of a door. In this case, you were acting as an antibody, the door was a pathogen, and the antigen was the handle of the door.

In an indirect ELISA antibody test, a sample is taken from a patient, which you may have experienced if you've gotten a nose swab at a COVID testing site. For antibody tests, this sample is often blood. If this person was/is infected, they will have developed antibodies that should be present in the sample.

First, a well is prepared with a lab-made antigen. Any antibodies made by someone who has been infected will recognize this antigen. For COVID testing, the lab-made antigen is a protein that the virus makes. Don't worry, the virus itself isn't there, just a small piece of it. It's harmless!

Second, the sample is added. If the COVID antibody from the patient is present in the sample, it will bind to the antigen. After this step, the well is given a wash. This removes anything that isn't the COVID protein, or the antibody that is bound to it.

Third, a secondary antibody is added. This antibody is specially made by a lab, and will attach to the first antibody. Weird, right? In this case, the antigen for the secondary antibody is actually a part of the COVID antibody! The secondary antibody also has an enzyme attached to it. No need to worry about what an enzyme is, but remember it's there for the next step. After this, another wash is given, and everything that isn't bound together is removed

Finally, a chemical is added. The enzyme attached to the secondary antibody from the previous step has the ability to turn this chemical into a certain color or make it fluoresce under UV light, depending on the enzyme. If the solution changes color, we know that the enzyme on the secondary antibody must be bound to a COVID antibody from the patient sample, meaning that the patient was previously exposed to SARS-CoV-2.