ABC’s of COVID testing
It can be confusing to try to make sense of the different tests out there for Covid-19. PCR, Antigen, rapid tests, antibody tests. Some are nasal swabs, some saliva, some require a blood draw. Some results come back in minutes, other’s days and some up to a week. What does it all mean and how do you choose the right test for you?
First, a quick lesson in virology. A virus is made up of genetic material surrounded by a capsule. This capsule has protein particles attached to the surface that enable the virus to attach and enter a host cell, take over the host cell’s reproductive machinery and create more viruses, which then burst out of the host cell, destroying it and going on to infect more host cells. We humans encounter millions of different viruses just about every day. Fortunately, we have an amazing defense called our immune system. Our immune cells recognize that the surface proteins on the virus capsule do not belong to us and quickly mount an attack to destroy the virus. Our immune cells create antibodies against those proteins which will then remove the offending virus from our bodies.
Now that you know how a virus works and how our immune system attacks it, the types of tests out there will make a lot more sense.
We know that Covid-19 typically enters our bodies through our nasal passages and mouth. Early on in an infection virus particles will begin attacking the cells that line our nose and mouth. By scraping some of those lining cells we can check for the presence of a virus in two ways. We can look for the surface protein on the virus capsule which is called an antigen protein, or we can look for the virus’s genetic material.
The Rapid Antigen Test
The rapid antigen test detects the presence of those surface proteins on the viral capsule. This test is done by collecting a nasal swab or some saliva. This test does not get sent to a lab. It can be run immediately and takes about 15 minutes to get the results. Sounds almost too good to be true. Well, that’s sort of the case. While very convenient it is not fully accurate. Accuracy can vary from 50-70%. It is more accurate if the result is positive than negative, which means if your rapid antigen test is positive, you likely are infected with Covid. However, if you test negative there is a chance you could still be infected. Please note that there have been false positives reported as well.
The rapid antigen test is a good screening tool. It’s a good test to get if you have been exposed to someone with Covid or spent time in a high risk setting (a large crowd without masks on or indoors with strangers without masks on) and have no symptoms. If you have mild symptoms your doctor may recommend starting with the rapid antigen test. A new nasal swab test just became available that can check for Covid-19 as well as Influenza A and Influenza B, all of which can present with similar symptoms. This test will be extremely helpful when the Influenza season is upon us.
PCR test
PCR stands for polymerase chain reaction. This is a test that looks for the genetic material inside the viral capsule. The specimen is obtained from a nasal swab or saliva and is typically sent to a lab for processing. There are some centers that preform the test on site. This test typically takes several days to come back, although it can take up to a week depending on how many specimens the lab must run. This is a very accurate test and to date, the most accurate test for diagnosing acute Covid infection.
The PCR test is used for diagnosing Covid-19. If you have symptoms of Covid or a significant exposure your doctor may recommend a PCR test. If you have mild symptoms and have a negative rapid antigen test you may still want to get a PCR test to be sure you are truly negative.
Antibody test
Our immune system makes different types of antibodies when it encounters the Covid-19 virus. These antibodies circulate in our blood stream. The antibody test is a blood test which looks for antibodies against the Covid virus. The presence of Covid antibodies simply means someone has been exposed to Covid in the past. It does not tell us when that person was infected or if they are currently still infected and contagious. Unfortunately, the experts do not know yet if these antibodies will protect us from future infection with Covid and if so for how long. For these reasons, the antibody test is not currently recommended for screening, diagnosis or confirming immunity to Covid. It simply verifies that someone has been infected in the past.
Here’s a simple breakdown to help you decide which test to get:
No symptoms AND Potential exposure - Rapid Antigen test
Mild symptoms AND no known exposure - Rapid Antigen test
Mild symptoms AND Potential exposure - Rapid Antigen test and/or PCR test
Moderate symptoms WITH OR WITHOUT exposure - PCR test
Uncertain if previously infected with Covid - Antibody test