I’ve been asked lately a lot of questions around COVID-19 testing. I know a lot of the information out there can be confusing – let me attempt to explain what the currently available tests are and what their results mean.
Plus, we’re excited as a clinic to be able (once again) to offer rapid COVID-19 testing! It’s a long story, but we’re back and ready to safely and quickly provide you diagnostic feedback if you wish to be tested for this novel coronavirus. Visit our Rapid COVID-19 Testing page to sign up for your test.
Before we jump in, a little primer on terminology so that we’re on same page. An antigen is an infectious particle like a virus or bacteria and an antibody is your immune system’s response to this antigen.
There are two main kinds of tests to consider: Antibody Tests and Diagnostic Tests.
When a virus enters your body, your immune system catches it and shows it to a specific immune cell called a B cell. These B cells examine the virus very closely – particularly examining the virus’s three-dimensional structure. The immune cells then go to work –making a protein called an antibody that mirrors the examined virus structure then binding the antibody to the virus – basically, to bind it up under lock and key. Once this process has wrapped, the immune system makes billions of copies of these antibodies and releases them into your blood to grab all of the viral antigen and lock them up – hopefully, finding them before the virus has infected other cells.
Sounds complicated…it is, and it takes time for the exam/construction/pairing to happen. A mature antibody called an IgG can take up to two weeks to be in production. In the meantime, an immature form called an IgM is created – it doesn’t fit so well to the structure and is a work-in-progress. These IgMs are a short-lived bridge to the better constructed and more mature IgGs. Sometimes we look for both forms to determine what stage of infection a person is in. Often, IgMs start being produced within two to three days of infection. As mentioned, the IgGs may not be present for up to two weeks but can be long-lasting (which is good).
These antibody tests are best used for determining if you have had prior infection and mean you may now be immune. Unfortunately, this doesn’t work so well in COVID-19 because even these IgGs don’t last that long – and up to one third of those infected will not develop any antibodies at all! This is a unique situation that sets these coronaviruses apart from most other viruses. In my clinic we have stopped recommending these tests because they don’t provide much useful data.
There are two main diagnostic tests to consider one is called a Molecular Test and the other an Antigen Test. A molecular test requires the virus to be broken open and its RNA (genetic material) to be released, copied millions of times, and then analyzed by a machine. This is pretty intense work and often requires a serious lab and well-trained people. It is quite accurate and is right about 96% of the time. Unfortunately, this type of testing can often take several days to return.
The second kind: antigen tests work by again going back to that invading three-dimensional structure and looking for a very specific pattern that we know is the COVID-19 outer capsule. A virus’s outer capsule is akin to its fingerprint and these tests can be very sensitive as well. The Quidel Sophia Platform has the ability to accurately predict infection 94.7% of the time.
We use this Platform in our testing – since it doesn’t require opening up the virus and reading RNA but allows us to return results within fifteen minutes! Thus, we are using diagnostic antigen tests to rapidly provide our patients results!
I hope this helps to explain this a little better. I’m including a link to the FDA site which has a video and a more extensive explanation of these concepts.
Knowledge is power and getting solid information can be difficult right now. Please take the time to look at some of my other blogs. The more you know the better prepared we will all be.
Nicholas Beaulieu, MD