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What can coronavirus antibody tests tell us? What we know so far

A new test that boasts nearly 100% accuracy has recently been approved, but debate still surrounds how useful such tests might be for both populations and individuals.

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Antibody testing looks for evidence that a person has been infected with the coronavirus SARS-CoV-2, but not the virus itself.

James Martin/CNET
For the most up-to-date news and information about the coronavirus pandemic, visit the WHO website.

Antibody tests, which are designed to show if you've ever had COVID-19 even if you never had any symptoms or knew you were infected, are often touted as key to bringing about the end of social distancing and reopening of the economy. A positive result could mean you might now be immune to the coronavirus and can possibly be around others without spreading illness, but debate about such tests' reliability and accuracy continue to beleaguer discussions about their usefulness. 

This month, a coronavirus antibody test designed to be highly accurate by biotech giant Roche received approval from the FDA as well as from a similar regulatory agency in the UK, Public Health England. Although many who advocate for expanded testing in the fight against the coronavirus pandemic may welcome the new test, which the company claims has a nearly 100% accuracy, serious questions remain about what the results from such tests mean for both the population at large as well as individuals who take them.

With so many different blood testsnasal swab testsdrive-through testing and at-home tests, keeping track of what's what can get confusing. Antibody testing is one term, but you may have also heard "antigen testing" and "serology" -- are they the same thing? That's why we're here. We're going to lay out what antibody tests are and aren't intended to do, and what such tests can tell us about COVID-19, if anything. 

One more note before we get underway. This article is intended to be a resource to help you understand current coronavirus testing as presented by organizations such as the US Food and Drug Administration and Centers for Disease Control and Prevention. It isn't intended to serve as medical advice. If you're seeking more information about coronavirus testing, here's how to find a testing site near you (here's another way for Apple Maps users). Here's how to know if you qualify for a test and why there aren't any coronavirus at-home test kits yet. This story is updated frequently as new information comes to light.

What is antibody testing for coronavirus?

An antibody test is a type of medical test that could help doctors determine if you have ever been infected with the coronavirus, regardless of whether or not you ever felt sick. This is important because many who contract the disease are asymptomatic

Antibody testing does not, however, reveal whether you are currently infected with the virus, nor does it indicate whether you have recovered from it if you did have it. The test only shows whether or not at some point you had the virus -- nothing more, nothing less.

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Why is the antibody test such a big deal?

A positive antibody test result usually means you're immune to the disease being tested for. Although researchers don't know enough about COVID-19 yet to be able to say for sure whether you'll be immune, the hope is that people who have recovered from the disease won't be able to catch it again, or, for that matter, infect others. 

If that turns out to be the case, once a high enough percentage of the population has developed immunity to the coronavirus, a form of indirect protection called "herd immunity" might shield those who haven't been exposed yet from getting the disease -- and help usher in an end to the pandemic.

Can antibody tests tell if you're immune to coronavirus?

With other diseases caused by coronaviruses -- like SARS and MERS -- a positive antibody test usually indicates some degree of immunity. However, the World Health Organization has warned that scientists don't know enough yet about this new coronavirus -- which is technically called SARS-CoV-2 -- to be able to say one way or the other. They're working on figuring it out.

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How does antibody testing work?

Antibody testing looks for proteins in the blood, called antibodies, which are left over after your body fights off a disease. When your immune system detects a new infection, your body starts producing antibodies, which it then trains to fight that specific invader. These antibodies figure out the invader's weaknesses, then neutralize, destroy and ultimately remove it from your body.

After it's gone, your body continues producing antibodies in case it ever comes back. That's what the coronavirus antibody tests look for -- the leftover antibodies your immune system produced to fight the coronavirus.

Where can I get a coronavirus antibody test? 

For now, you'll have to start by talking to your doctor or another health care practitioner who is licensed to order lab tests. Guidelines vary by provider and by state, but generally you have to have been asymptomatic for one to two weeks (including the day of the test). 

Up until last week, antibody tests have not been widely available in the US, so health care professionals and first responders have been given priority. But starting April 27, you can get an FDA-authorized coronavirus antibody test at LabCorp facilities or doctors' offices and health care facilities staffed with a LabCorp technician (there are thousands nationwide).

Right now, only the LabCorp test and three other antibody test kits have been authorized by the FDA under a rule that allows medical devices to be used during a public health emergency prior to FDA review. Under a similar emergency policy, the FDA is also allowing the use of test kits from nearly 100 other manufacturers, but some experts warn you shouldn't trust such tests until they have been vetted more thoroughly. 

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What is an antigen?

An antigen is a substance that usually comes from your environment and makes you sick when it gets inside your body. Common antigens include bacteria and viruses. Antigens trigger your immune system to produce antibodies, which fight back.

Antigens can get into your system much the same way you bring the substances you need to survive into your body. You can inhale airborne antigens into your lungs when you breathe, for example. Or you can bring antigens into your mouth when you, say, pick up an infectious substance like the coronavirus off a surface with your hands, then touch your face.

Antigens can also get into your body through your ears, eyes and nose. Rarely, but occasionally, you can absorb them through your skin.

How is antigen testing different from antibody testing?

An antigen test looks to see if you currently have the disease by searching for genetic information unique to a particular virus or bacterium. It tells doctors whether you are currently infected or not, but not if you were infected in the past and have since recovered.

Conversely, an antibody test only shows whether or not you've had the disease in the past. It can take up to two weeks for antibodies to be detectable in your blood -- usually long after the virus has been defeated and an antigen test would come back negative.

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What is serology or a serology test?

Serology refers to the study of blood serum, and the vast majority of serology testing is done to detect antibodies. Other body fluids, like saliva, can be tested too, but that's because they contain trace elements of blood, which is what's actually being tested.

Serology tests can also determine blood type when donating blood or receiving a transfusion. They can be used to measure the levels of pharmaceuticals present in the bloodstream, during a drug trial, for example. But most of the time, when experts use the phrase "serology" or "serology testing," they're talking about antibody tests.

Although increased antibody testing may help hasten the end of lockdown, it's not the only thing that can speed the return to normalcy. Here's a look at what needs to happen before shelter-in-place orders begin to be lifted in the US. If you or someone in your home contracts COVID-19, here are the steps you need to take to avoid spreading the virus further. And here's what to do to stay safe when you have no choice but to venture out in public.