What Does a Positive Coronavirus Antibody Test Result Really Mean?
Testing positive for COVID-19 antibodies may not necessarily mean you're in the clear for a future coronavirus infection.
Whether you've recently felt sick or not, chances are you've entertained the idea of getting tested for coronavirus (COVID-19) antibodies.
If you've been following news about the pandemic, you probably already know that COVID-19 testing, in general, can (still) be hard to come by in some parts of the U.S. As a result, many experts have agreed that, if you think you may be infected with COVID-19, but aren't experiencing severe symptoms and aren't considered to be at a high risk of developing serious complications, it's best to simply stay home, rest, and self-isolate as though you do have COVID-19. (Related: When, Exactly, Should You Self-Isolate If You Think You Have the Coronavirus?)
But what's the deal with coronavirus antibody testing? Is it just as difficult to access as coronavirus diagnostic testing? How reliable are the currently available COVID-19 antibody tests really? And are they actually going to help everyone return to some semblance of "normalcy" anytime soon? Here's what you need to know about coronavirus antibody testing.
First, what is an antibody test?
Antibody blood tests measure your body's immune response to certain health conditions (including, but not limited ti COVID-19), either through a blood draw or finger prick. To be clear, a coronavirus antibody test is different from a coronavirus diagnostic test; the latter involves a nasal swab or saliva sample to detect a current infection, according to the Centers for Disease Control and Prevention (CDC). Meaning, antibody tests can tell you whether you've already been infected, but they can't confirm that you have an active infection.
There are two types of antibodies these blood tests can measure: IgM and IgG. IgM antibodies typically develop within a week or two of the start of your infection (but, again, this doesn't confirm whether the infection is still active at the time of your test result), says Emily Stoneman, M.D., an infectious disease specialist at the University of Michigan in Ann Arbor. These antibodies stick around in your body for about five weeks following the start of the infection, after which point they aren't detectible in your blood, she explains. They can indicate that you've either recently been (and are maybe still) infected with a virus, or they can indicate that you've recently recovered. IgG antibodies, on the other hand, similarly signify that you've been infected in the recent past, but they also indicate that your immune system has since cleared the infection, says Dr. Stoneman. These antibodies can form within the first week or two of infection as well, but they typically stick around much longer than IgM antibodies—possibly for weeks, months, years, maybe even for life, explains Dr. Stoneman. (Related: Everything You Need to Know About Coronavirus Transmission)
The presence of either type of antibodies—even if you never experienced any coronavirus symptoms, at least that you know of—means you've been exposed to the virus (or, technically, a coronavirus, not necessarily COVID-19—more on that soon). And while these antibodies might protect you from future infection, that's not a guarantee.
How reliable is coronavirus antibody testing?
Antibody testing is one of many recommendations in the federal government's plan for reopening America (contact tracing is another reopening measure). But as of now, it's not as simple as testing positive for coronavirus antibodies and immediately going back to work, says Erika Schwartz, M.D., an internal medicine physician in New York City.
For starters, remember that antibodies take a couple of weeks for the body to develop—meaning false-negatives are technically possible. However, the bigger issue that many healthcare providers are currently reporting is a significant number of false-positive tests, notes Dr. Schwartz. Several different factors can lead to a false positive coronavirus antibody test result (including the sensitivity, accuracy, and reliability of the test itself, among other things). One possible explanation could be that you've recently had one of the four known human coronaviruses that cause the common cold, or one of the two coronaviruses that cause severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS), respectively, according to the World Health Organization (WHO). In other words, testing positive for coronavirus antibodies could simply mean you've built up antibodies to other types of coronaviruses and not necessarily COVID-19, according to the CDC. TL;DR: "If someone receives a positive test result, they need to be tested twice to ensure it's not a false-positive," explains Dr. Schwartz.
Anecdotally, Dr. Schwartz has also seen cases in which patients have tested positive for COVID-19 antibodies while their housemates have tested negative. That discrepancy raises questions about not just the reliability of the tests, but also whether different people just have different immune responses to the virus, she says.
"What we're seeing from a lot of locations from around the country that have been doing more widespread antibody testing is that the percentage of people who have a positive antibody test is pretty low," says Dr. Stoneman. Experts are still learning more about why that number appears to be lower than expected. But for now, it seems to indicate that, even in areas where there has been a widespread transmission of COVID-19, many people may still not have been infected with COVID-19, let alone had the opportunity to build up any antibodies, explains Dr. Stoneman. (Related: Can the Coronavirus Spread Through Shoes?)
"Right now, we're very far from actually knowing what antibody testing really represents, as we don't have historical data to go on," adds Dr. Schwartz. "With other diseases, you can sometimes develop antibodies for life, or for a limited period of time. With COVID-19 we don't know because it's new, and we need time to figure out how long immunity may last."
Does having coronavirus antibodies mean you're immune to COVID-19?
At this point, the only sure thing a positive coronavirus antibody test can demonstrate is an immune response to a coronavirus (and, again, not necessarily COVID-19). The presence of antibodies could mean you've built an immunity to SARS-CoV-2 (the virus that causes COVID-19), but experts can't say for sure because the virus is still so new and research is limited so far.
"We don't fully understand whether a positive antibody to COVID-19 indicates you're really immune, or if you could get re-infected if you're potentially exposed again," says Dr. Stoneman. "If it does turn out that there's some immunity, we don't know if that immunity will last months or years. It's really too soon to understand what these antibody test results mean. As we go on over the next few months and start to see another wave of infections, we'll have a better sense of the risk of reinfection."
So for now, at least, a positive coronavirus antibody test simply means you were likely exposed to a coronavirus (which might have been SARS-CoV-2) and that your immune system responded to the infection, explains Dr. Schwartz. "And, for now, you should be counted as someone who is potentially 'temporarily immune,'" she adds.
So, who should get an antibody test?
Understandably, efforts are focused right now on testing people in high-risk professions who are more likely to be exposed to COVID-19, explains Dr. Stoneman. That includes healthcare workers, first responders, and others working in public-facing jobs where they have a lot of interaction with people outside their home. That said, some cities that aren't struggling with a shortage of coronavirus tests (diagnostic or antibody) are extending testing services to the general population. Be sure to check with your local health officials about what type of coronavirus testing is available in your area.
Another area of interest for antibody testing: those who have received a positive COVID-19 test and have since fully recovered, as they may be eligible to donate blood plasma. Although the current research is limited here as well, experts believe that donated plasma from someone who was previously infected with COVID-19 and has measurable antibodies in their blood may be a viable treatment option for those who are severely ill with a COVID-19 infection (i.e. those in an intensive care unit and possibly on a ventilator). (Related: Your Guide to Donating Blood During Coronavirus—And After)
Where can I get an antibody test?
The good news: Coronavirus antibody testing is expected to become more widely available to the general public in the coming weeks and months, says Dr. Schwartz. You'll soon likely be able to request an antibody test without a prescription at a lab testing center (such as LabCorp or Quest Diagnostics).
Keep in mind: At this time, there are no FDA-approved coronavirus antibody (or diagnostic) tests. Many of these tests (both diagnostic and antibody) have been granted emergency use authorization (EUA) by the agency while the approval process is ongoing. EUAs are often issued during public health emergencies to allow for expedited use and distribution of "potentially life-saving medical products to diagnose, treat, or prevent the disease" (in this case, COVID-19), as long as those products meet certain criteria, according to the FDA. But some tests (both diagnostic and antibody) on the market haven't been vetted by the FDA at all, and experts say there's no way of knowing how reliable or accurate such tests are. The FDA is cracking down on these non-vetted tests by requiring them to meet tighter standards of accuracy testing quality.
How long it takes to get coronavirus antibody test results depends on which testing method you receive and where it's processed. With a finger-prick test, you could have results in 15 minutes, but a serology (blood draw) test may take longer because it involves getting blood taken and then sent to a lab for processing, which could take three to five days.
Since antibody testing isn't widely available yet, experts can't confirm whether it will generally be covered by health insurance or programs like Medicare or Medicaid. (Expenses for the test might also be eligible to submit to an HSA, FSA, or similar health reimbursement account—you'll have to check with your provider to know for sure, though.) In terms of estimated out-of-pocket costs, a finger-prick test might be around $30, while a blood draw could be $100 to $130, says Dr. Schwartz. (Related: What Is Telemedicine, Exactly?)
The Bottom Line On Coronavirus Antibody Tests
"Getting a positive coronavirus antibody test can be somewhat reassuring to people because of the possibility of immunity, [which] may last for at least a few months or longer, which may make you feel a little better about going back out in public when things begin to reopen in the next few weeks or months," says Dr. Stoneman.
But again, experts say it's still complicated to understand what a positive coronavirus antibody test truly means at this point. One thing that's for sure: It doesn't guarantee immunity to COVID-19. Meaning, you can't assume you're protected from future exposure (and potential infection), or that you're not at risk of passing the virus to others.
As experts continue to try and understand coronavirus antibody testing more and roll it out to the public, it's important to continue practicing all the coronavirus prevention measures you've likely perfected by now: regularly washing your hands, following federal and state guidelines about social distancing and stay-at-home orders, wearing a cloth face mask in public, etc.
"Unfortunately, we are probably going to be stuck with some degree of social distancing for quite some time, which people are getting tired of," admits Dr. Stoneman. "But it's important to prevent another wave of infection that we may see this summer once things start to open back up. We still need to be very cautious and take steps to protect ourselves and others."
The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it’s possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.