COVID-19 Antibody Tests: What You Need to Know

There is currently no evidence that people who have Coronavirus antibodies are protected from a second infection

With Kaberi Dasgupta MD and Leanne De Souza PhD

COVID-19 antibody tests are not as surefire as they may seem.

 

As a nation, we are growing restless. Summer is tantalizingly beckoning us all outdoors. But, more than that, the economy is shuddering under the pressure of our very necessary social distancing restrictions through the COVID-19 pandemic. So, it’s no wonder that people, governments, businesses, and communities are all looking for antibody tests to be the key that could unlock all of us from our long quarantine. But are they?

What is an antibody test?

Unlike the rt-PCR test, in which a swab is inserted up the nose to collect mucus and detect if you have the COVID-19 virus, an antibody test uses blood to detect if your body has developed antibodies to fight the virus. Antibodies are y-shaped proteins that look for and attack bacteria and viruses. It takes two or three weeks for an infected person to develop antibodies to the COVID-19 virus.  So, people are advised to wait 10 days after virus symptoms leave before taking an antivirus test.

Many hope that developing these antibodies will confer immunity, and once a person has that immunity, they’ll be able to reenter public life without worry of contracting the virus again. But, of course, the reality is much more complex. For one thing, the United States has been flooded with a deluge of poor-quality antibody tests with little guidance for navigating your way to a reliable one. And, once you do find a reliable test, there is still a great deal of uncertainty as to whether the presence of antibodies renders immunity. 

How accurate are COVID-19 antibody tests?

This really depends on which test you take. There are currently two classes of tests. The first is the so-called rapid response or point-of-care test, which can be taken at doctors' offices or workplaces. These tests are designed to tell you if any COVID-19 antibodies are present in your body, with a yes or no answer.

The World Health Organization has advised the public against using these tests for making decisions about their own health. “At present, based on current evidence, WHO recommends the use of these new point-of-care immunodiagnostic tests only in research settings. They should not be used in any other setting, including for clinical decision-making, until evidence supporting use for specific indications is available.”

The second class of tests tells you how many (if any) antibodies are in your body. Rather than taking blood from a pin prick, these tests require a greater quantity of blood taken intravenously, and that sample is then sent to a lab for analysis. Because these lab tests are more complex and done in a controlled setting, they tend to be more accurate. But there is still room for inaccuracies such as cross reactivity, which is when a test picks up on common cold coronaviruses and mistakenly misidentifies them as COVID-19-related.

At the beginning of the outbreak, the FDA attempted to regulate antibody tests entering the American market. Under pressure to move faster, the agency loosened restrictions in mid-March, allowing manufacturers to release tests to the public so long as they notified the FDA, did their own validation, and labeled their tests as approved or not approved by the FDA. Naturally, this caused a great deal of confusion.

At one point, there were over 100 tests available in the US that the FDA hadn’t vetted, many of poor quality from disreputable companies. A consortium of researchers created The COVID Tracking Project to test the reliability of antibody tests (among other important metrics). They found that only three of the 14 tests they evaluated delivered consistently reliable results. So far, only one of the tests never delivered a false positive, and two of the tests were correct about positives 99 percent of the time.

Mayo Clinic doctors tested 19 different tests. 4 out of the 9 rapid tests failed their standards, 4 of the 10 lab tests got an “A-plus” rating, and “two or three” of them failed. The FDA eventually tightened restrictions, but the damage was already done, and the poor-quality tests are out there. This past weekend, the CDC issued a new guidance stating that fewer than half of the antibody tests are correct.

What do the antibody test results mean… really?

Assuming that the test results are accurate, all they tell us is whether or not your body appears to have developed proteins in response to the virus. A complex lab test can give you an idea of how many antibodies you may have. And that’s about it.

We still don’t know much more about what the results mean

Even if a test shows you may have developed antibodies to the COVID-19 virus, that doesn’t necessarily mean you’re immune. This virus is still very new, and there’s still a lot we don’t know about it.

We don’t know how protective those antibodies are, under what circumstances, and for how long. We don’t have a reliable, consistent way to tell how well antibodies will perform their function. In other words, just because you have a lot of antibodies doesn’t necessarily mean they’ll do their job of protecting you.

The WHO cautions, “There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.”

Dr. Kaberi Dasgupta, professor of clinical epidemiology, endocrinology, and metabolism at McGill University, cautions that testing isn’t as straightforward as you’d think. Especially with the rapid-result tests, reducing it to a yes/no question doesn’t give us a full enough answer. She compares the COVID-19 antibodies to the flu. “We know for the flu, every year we get vaccinated because every year there’s a variation in the virus.” There may be some carryover from one year to the next, but not enough to be protected.

In addition to these concerns, you also need to think about test results in the context of real life. Right now, the prevalence of the Coronavirus in most places in the US is around 1-5 percent, meaning that’s the percentage of people who have been exposed to the virus. (In other locations like New York City, the prevalence rate is believed to be as high as 25 percent.)

Here’s the tricky part: the lower the prevalence of COVID-19 in your community, the higher the chance for error in the antibody test. This is because there’s a lower chance that you’ve been exposed to the virus, so there’s a higher chance a positive result is due to cross reactivity in the test.

Is an antibody test worth taking?

Are you looking for assurance that it’s safe to mingle with the public? If so, the answer is no. An antibody test, even a highly reliable one, is not worth taking in order to inform your personal health decisions.

Dr. Leanne De Souza, Course Instructor in the Department of Biology and member of the Obstetrics and Gynaecology Research Committee of the Women’s Health Care Centre at the University of Toronto, says she doesn’t believe we have enough information to make definitive decisions about how long people are protected after an infection.

“We don't know enough about this virus, and we don't know enough about how it mutates and how it reacts with other conditions or other viruses, even,” she says, adding that we can expect people with chronic conditions or underlying complications to be more vulnerable when and if they contract the virus.

“Antibody testing is rather complex because it's not just, do you have antibodies? But also, how long do they protect you, and is that different for different populations? There are so many layers to this issue, that I think that it'll take time to really rely on antibody testing. It's still early days for that.”

What tests can do is measure how many people in a given population may have been exposed. That’s helpful for researchers. But again, that doesn’t necessarily indicate that it’s safe for that community to lift their restrictions.

As for the cost, under the federal Families First Coronavirus Response Act, antibody testing is supposed to be free. But, some labs offering “consumer-initiated” testing still charge a fee, typically around $100. Imagine paying $100 out of pocket for a test that guarantees you nothing.

What are the most reliable antibody tests?

At this point, a small handful of companies are producing lab tests claiming specificity and sensitivity rates that are both above 95 percent, which means they show almost no false positives, nor false negatives. They include:

  • Epitope Diagnostics IgG Elisa (not the IgM): specificity rate 100 percent; sensitivity rate 100 percent
  • Roche Elecsys Anti-SARS-CoV-2: specificity rate over 99.8 percent; sensitivity 100 percent
  • Abbot Laboratories Abbot Sars-CoV-2 IgG: specificity 99.5 percent; sensitivity 100 percent
  • DiaSorin Liasion SARS-CoV-2 IgG: specificity 98.5 percent; sensitivity 97.4 percent

There are two main antibodies that can be tested: IgM and IgG. The IgG is produced later into an infection and appears to stay active longer. Keep in mind, we are trusting these companies’ own claims about their respective tests’ accuracy.

Currently LabCorp uses Abbot and Roche antibody tests, and Quest uses Abbot and PerkinElmer’s Euroimmun tests (which have a specificity rate of 94.8 percent and sensitivity of 85.4 percent). Labs will not always disclose to patients which test they are getting.

Whatever you do, do not order antibody tests online or buy them from the drugstore. Even if your doctor recommends a testing lab, ask a lot of questions, especially about the accuracy rate of the test.

Is it safe to receive your ongoing care for other conditions at the hospital?

Now that you know that even if you’ve had a reliable test showing you have loads of coronavirus antibodies, you’re not necessarily immune, what do you do about your regular treatment for diabetes or other conditions?

Bottom line: continue to get the care you need.

Dasgupta acknowledges that it’s scary to know a highly-transmissible virus associated with mortality is out there. She has heard of people with heart attack or stroke symptoms avoiding the hospital out of fear that they would contract the virus. “This you must not do. Go!” Likewise, she advises against delaying routine care.

“It’s been a bit of a challenge managing any outpatients with chronic conditions for diabetes at our institutions,” says Dr. Dasgupta. She and other doctors have pivoted to telehealth as much as possible. But now that it’s been about three months since the coronavirus outbreak, she’s noticed people are reluctant to come in for their A1C testing. Some patients are relying on their blood glucose monitoring, but not everyone does this routinely.

Dr. De Souza emphasizes, “But I will say that timely access to care is so critical for people who are self-managing at home.” She notes that pregnant women with gestational diabetes, for example, may not yet be accustomed to the routines of self-monitoring. And they risk exacerbating a serious condition that could also be life-threatening.

Both De Souza and Dasgupta recommend weighing the risks of coming in for a test or other care with your doctor. And they point out that hospitals are observing heightened policies to protect everyone. De Souza adds that your usual care center’s services may have even moved to a safer location.

Set yourself up for more self-monitoring and virtual care

This is all the more reason for people with chronic conditions to set up virtual care to minimize the need for outpatient visits. Do you have your blood glucose monitor, a home blood pressure measurement device, and a digital scale? “If they have all that paraphernalia at home, and if we are set up technology-wise to upload those data without too much effort,” Dasgupta says, “then I think we could do a lot more with people being at home.” Older patients would also need caretakers or family members who can help.

“It's even more important now to do basic things such as eating healthy, getting some exercise, making sure that you have the right supply of your strips, and that your pump and your glucose monitor, and your CGM are all in working condition,” says De Souza. Have recurring prescriptions automated (many drug stores deliver) and have wound care handy.

How to protect yourself if you do need outpatient care during COVID-19

When it comes to protecting yourself, the same rules apply as any other situation when you’re going out in public. Keep six feet away from other people whenever possible. Avoid anyone showing symptoms of any kind. Wear a mask when you are in public places. Dasgupta says they have an added benefit of prompting us not to touch our faces. Wash your hands thoroughly.

Dasgupta also notes that having diabetes doesn’t necessarily mean you’re at risk for worse outcomes; it’s more that not having your blood sugar well-controlled puts you at higher risk because there seems to be a connection between blood sugar and how well white blood cells work to fight off the virus. So, working with your healthcare provider to control your blood sugar and maintain good health habits are both important parts of minimizing your risk for COVID-19.

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