So, Here's the Deal with COVID Antibody Tests
Namely, how reliable are the results – and what should you even do with them?
When antibody tests first became widely available, my group texts were buzzing with questions like: Should I get one? Can I trust that the results are accurate? And, if I do have the antibodies... what does that actually mean? Am I definitely protected from getting the coronavirus again?
Now, there's a whole new set of concerns swirling about antibody tests. Last week, the FBI warned that fake antibody tests are being used by fraudsters to steal social security numbers and personal health information. Then, a new 60 Minutes investigation revealed federal officials knew many COVID-19 antibody testing kits had flaws, but allowed them to be released anyway. So, yeah, it's hard to keep up.
If you're having trouble making sense of the latest antibody test headlines — or deciding whether it's even worth it to get an antibody test right now, especially as the country re-opens and coronavirus cases spike — we have you covered. We spoke with infectious disease experts to unpack what we know (and don’t know) about the accuracy of antibody tests currently available, whether you should get tested, and what you should actually do with the results.
What’s an antibody test — and how is it different from a test for COVID-19?
If this is the first time you’re hearing about antibody tests, here’s the gist: Antibody tests, also referred to as “serological” tests, check the blood for the presence of antibodies, aka proteins the body makes in response to an infection.
Antibody tests can be broken down into two general types: qualitative, which gives you a yes/no result — yes, you had COVID-19, or no you didn't — and quantitative, which tells you how much of an antibody you have, explains Sandra Kesh, M.D., infectious disease specialist and deputy medical director at Westmed Medical Group in New York. And, yes, antibodies also usually provide some level of protection or immunity from getting that infection again.
So, in the case of the current pandemic, antibody tests can tell you if you had a past infection with SARS-CoV-2, the virus that causes COVID-19, but they aren’t diagnostic. If you think you currently have COVID-19, you’ll need a nasal swab, which tests genetic material and identifies if you have an active infection.
Where can I get my antibody test — and how do I know I'm not being scammed?
At this point, antibody tests are widely available through healthcare providers, urgent care centers, pharmacies, and pop-up or drive-through testing centers across the country. In most states, you can simply make an appointment online or walk in, and insurance will usually cover the cost, says Andrea Amalfitano, D.O., Ph.D., a professor of microbiology and dean of the College of Osteopathic Medicine at Michigan State University. In some cases, you must first get a prescription from your physician. If he or she believes there's sufficient reason to think you had COVID-19 recently (and weren’t tested for the virus), they can give you the go-ahead.
Both experts recommend getting tested through your own physician when possible, since they can help you interpret the results based on your individual circumstances and prevent confusion. But there's another reason you're better off going to a known source: Last week, the FBI warned of scammers marketing fraudulent and/or unapproved COVID-19 antibody tests in order to obtain personal information and personal health information for identity theft schemes.
The FBI lists the following potential indicators that something is amiss:
- Claims of FDA approval for antibody testing that cannot be verified
- Advertisements for antibody testing through social media platforms, email, telephone calls, online, or from unsolicited/unknown sources
- Marketers offering “free” COVID-19 antibody tests or providing incentives for undergoing testing
- Individuals contacting you in person, phone, or email to tell you the government or government officials require you to take a COVID-19 antibody test
- Practitioners offering to perform antibody tests for cash
Basically, if you're being offered a test at all, say no. You should be the one seeking out an antibody test, ideally from your own primary care physician. "As a general rule, most medical groups, providers, and hospitals now have enough testing available, so that you can reliably find something," Dr. Kesh explains. "I would be weary of any pop-up situations that have been appearing."
If you can't see your own provider, use a known laboratory approved by your health insurance company to provide the antibody testing, the FBI advises. Be sure to check the FDA website for an updated list of approved antibody tests and testing companies — and don't share personal or health info with anyone other than known and trusted medical professionals.
There's another red flag to watch out for: "I would avoid any testing place that claims to give you a 100% guaranteed result," Dr. Kesh says. "There are no 100% reliable antibody tests on the market at this point in time. This should be seen as a red flag if you’re looking at options." Which brings us to our next point...
How accurate are the COVID-19 antibody tests available right now — and is the FDA reviewing them?
Back in March, the FDA took the unprecedented step of allowing antibody tests to enter the market without being reviewed — and hundreds of tests flooded the market. Then, in May, the agency required test makers to apply for emergency authorization (or EUA) and submit data to show their tests worked. However, the damage was done. And, to make matters worse, as 60 Minutes recently uncovered in a three-month investigation, "federal officials knew many of the antibody tests were seriously flawed but continued to allow them to be sold anyway." Uh, yikes.
So, while the quality and accuracy of antibody tests have improved significantly since the beginning of the pandemic, it can be hard to know which ones are 'best' Dr. Kesh says, since "we’ve never seen a situation where so many inadequately validated tests have hit the market."
What does this mean? You should check that your antibody test has this authorization from the FDA. Still, it's important to know that manufacturers are self-reporting their internal validation data (based on very small sample sizes) to the FDA — and just how much scrutiny these tests are under before they are released is unclear, Dr. Kesh adds.
But what about the CDC warning that antibody tests are wrong half the time?
Broadly speaking, the accuracy is determined by the test’s sensitivity and specificity: A sensitive test is less likely to provide a false-negative result and a specific test is less likely to provide a false-positive result, but no test is ever 100% sensitive and specific, Dr. Amalfitano says.
Here's where things get tricky: If COVID-19 has only affected a small percentage of people being tested, the false positive rate will be higher. This is why the CDC recently reported that antibody tests are wrong up to half of the time. And the problem is, many areas don’t actually know how much of their population has been infected, due to lack of resources or organization at the national level, per a new report from infectious disease experts.
Simply put: “It becomes a coin toss if you get a test in an area where they don’t know how much COVID-19 they have,” Dr. Kesh says. “It could be picking up antibodies for the common cold.”
This is important because antibodies are disease-specific. As the CDC puts it, “measles antibody will protect a person who is exposed again to measles but will have no effect if the person is exposed to mumps.” Right now, the vast majority of tests out there have the potential for cross-reactivity with other coronaviruses — meaning they are not 100% specific to COVID-19, she adds.
I received a negative antibody test — what does that mean?
If you got tested and were surprised to receive a negative result, it doesn’t mean with absolute certainty that you weren’t infected with COVID-19.
“It could mean that you were infected but didn’t develop antibodies the test is measuring, or the blood test isn’t picking it up because you didn’t make a measurable amount of antibody,” Dr. Kesh says. This could be the case if you had a low-grade infection, Dr. Amalfitano adds. A negative test result, despite prior COVID-19 infection, may be more common in immunocompromised patients due to a lack of, or delay in, the development of detectable antibodies, Dr. Kesh adds.
Another possibility: You got tested too soon. “It takes time for your body to make enough of the antibody to be picked up by the test,” Dr. Kesh explains. Antibodies start developing within one to three weeks after infection, according to the CDC, which is why experts recommend waiting at least two weeks after your symptoms have subsided before getting an antibody test. (On the flip side, “antibody levels typically stay high for months, sometimes even decades after infection with some viruses” — so there’s likely no such thing as waiting too long to get an antibody test, Dr. Amalfitano adds.)
Lastly, it’s possible your test simply wasn’t good enough to detect anything, Dr. Amalfitano adds. So… yeah, it’s far from black and white.
Does testing positive for antibodies mean I’m immune from future infection?
Accuracy questions aside, the biggest unknown right now is whether or not a (reliable) positive antibody test means you have protection from future exposure to the virus.
Per the CDC: “We currently don’t have enough information yet to say whether someone will definitely be immune and protected from reinfection if they have antibodies to the virus.” And if the antibodies do provide immunity, we still don’t know for how long it might last.
To be able to answer these questions, we need more sophisticated testing, Dr. Kesh says. “The problem is, the antibody tests we have now are not measuring the antibody involved in neutralizing the virus. None of the widely available tests can do that,” she explains, adding that such a test is still under development.
So, does a positive antibody test give me any reassurance?
With so many unknowns, a positive antibody test simply isn’t a get out of jail free card — and it shouldn’t change your actions when it comes to social distancing.
However, if you had symptoms or exposure to COVID-19 and your antibody test is positive (and you live in an area where there has been a high prevalence), it's likely you indeed had the virus at some point, both experts say. “I cannot tell [my patients] how immune they are and I can’t say if they’d be protected from another exposure, but it’s pretty reasonable to expect they’d have some immunity,” Dr. Kesh adds.
So should you even bother getting tested? “I would only get the test if you need to be able to do something you otherwise wouldn’t feel comfortable doing,” Dr. Kesh says. “For example, I tell my patients who have a parent or grandparent they need to take care of that they can [if they’ve tested positive for antibodies] — but to still wear a mask and practice all the proper hand hygiene.”
Bottom line, yes, a positive test can provide some level of peace of mind, but “it’s not going to give you the magical answer and clearance that people were hoping for,” Dr. Kesh says.
The coronavirus pandemic is unfolding in real time, and guidelines change by the minute. We promise to give you the latest information at time of publishing, but please refer to the CDC and WHO for updates.