Much of the U.S. is still in the thick of the COVID-19 pandemic, with little end in sight. Experts work around the clock to trace, research and develop testing and vaccination protocols to limit its spread and – hopefully – slowly eradicate the virus from our population. One crucial piece of this strategy involves antibody testing, which is different than the common, cringe-worthy “nasal swab.” Our scientific contributor, Heather Huntsman, Ph.D., CSSC, explains more below.
It’s hard to say whether there is more information out about COVID-19 than other topics, or if we simply just care more – and have more time – to consume headlines and studies. Regardless of the reason, it’s a lot. It can be overwhelming because while we want answers, there is yet to be any solid conclusions. It’s also hard to compare this pandemic to any other situation, as little is known about its trajectory, but we can clearly see its impact. Almost every decision I’ve made has been influenced by COVID-19 – and that only speaks to its impact on one person, let alone the world. That said, we’re continuing to move forward in fighting the virus through testing. Because of this, it’s important to clarify the difference between each type of test and what they are used for.
There are two main categories of tests that are important to be aware of.1 First, when most people think of testing for SARS-CoV-2, they think of those miserable nasal swabs. (Side-note: there are two commonly used terms for the virus: SARS-CoV-2 is the name of the virus whereas COVID-19 is that name of the disease caused by the virus.) In typical testing, a swab is collected and a lab tests for one of two markers: genetic material from the virus or parts of the virus itself. These tests are called “molecular and antigen tests,” respectively, and fall under the category of diagnostic testing.1 These test for active infections and are the most accurate within the first week of the start of symptoms, when the numbers of virus in your mucus membranes have peaked.2
The second category is called “antibody testing.” The most important thing to know about this type of testing is that it isn’t meant to be a diagnostic test.3 Rather than a nasal swab, these tests are blood-based, and are specifically testing the body’s adaptive immune response to the virus. After the virus enters body, primarily through our nose and mouth (which is why the diagnostic tests swab those areas), the virus increases in number (depicted on left side of the graph).4 When this occurs our body ramps up its defenses. The most targeted and specific way our bodies do this is through antibody production. Essentially, antibodies are little “tags” produced by our white blood cells that signal to the rest of our immune system to fight whatever foreign invader is tagged. So, as the number of antibodies increase in our blood, the number of virus particles in our bodies should decrease (depicted on the right side of the graph). Unfortunately, that takes time and energy and is the reason why the red line doesn’t increase until much later after the initial infection (i.e. day ~5 before the start of systems).5
So, if antibody tests aren’t meant to diagnose someone with active infection, what are they used for? That is a great question with a surprisingly straight forward answer. Antibody tests are designed to test for past infection, and are helpful for scientists and physicians that are studying the pathogenesis of COVID-19.2 It tells experts how the body responds to the virus, on what timeline, with what intensity, and most importantly, identifies whether someone has been infected – even if they haven’t shown any symptoms.5 Answers to these questions are important in guiding treatment and vaccine development. And although we still don’t have straightforward answers to some of the unknowns (whether reinfection is possible, or how long immunity lasts after infection3), studying the body’s response through tests like antibody testing at least provides valuable information that may help prevent the spread of the virus.
- Corona Virus Testing Basics, https://www.fda.gov/consumers/consumer-updates/coronavirus-testing-basics; Content current as of 7/16/2020.
- FAQs on Testing for SARS-CoV-2. https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/faqs-testing-sars-cov-2#serology; Content current as of 8/25/2020.
- Fang FC, et al. (2020) The Laboratory Diagnosis of Coronavirus Disease 2019— Frequently Asked Questions, Clinical Infectious Diseases, doi: 10.1093/cid/ciaa742.
- Serology Testing for COVID-19 at CDC, https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testing.html; Content current as of 5/23/2020.
- Burbelo PD et al. (2020) Sensitivity in Detection of Antibodies to Nucleocapsid and Spike Proteins of Severe Acute Respiratory Syndrome Coronavirus 2 in Patients With Coronavirus Disease 2019, The Journal of Infectious Diseases, 222(2):206-213. doi: 1093/infdis/jiaa273.
This article is not intended to provide medical advice. If you have any further questions, or would like to seek recommendations, contact your physician or healthcare provider.