What Is a Coronavirus Antibody Test—and Why Testing Matters
Everybody wants to know when stay-at-home orders will be lifted, but experts agree that’s unlikely to happen until widespread antibody testing has been carried out. While a nasal swab test can detect existing infection, a blood test can determine if a person has been exposed to the new coronavirus. Known as an antibody test or serology test, this may identify those who have recovered from infection and, potentially, have developed some degree of protection from reinfection (by demonstrating an "immune response" to the virus).
Whether you have the virus or not, this development in the fight against COVID-19 affects everybody—wide-scale antibody testing may be key to getting those stay-at-home orders lifted.
What Is Antibody Testing?
Antibodies are human proteins produced by the body to fight infection. “During an infection, the immune system custom-designs antibodies to recognize a specific part of the virus,” Craig Wilen, MD, an assistant professor in laboratory medicine and immunobiology at Yale University, tells Health.
In the case of the new coronavirus, the most important antibodies target the viral spike protein, which is the protein that binds to the human cell receptor and allows the genetic material of the virus to enter human cells and begin infection. “There are two types of virus-specific antibodies that are relevant for testing,” Dr. Wilen says. “The first is called immunoglobulin M (IgM). This antibody is made earlier in the period of infection and then goes away. The second is called immunoglobulin G (IgG), which is made after IgM, but lasts much longer.”
While there is some variability in timing between people, IgM lasts for weeks to months and is detectable after a week or two, whereas IgG lasts for decades and is detectable days to about one week after IgM. By detecting the different antibodies in a person’s blood, doctors are able to “date” when they had—or still have—the infection.
If My Test Comes Back Positive, Am I Immune?
Unfortunately, scientists don’t yet know whether a positive test means you’re immune or how long such protection may last. “There have been reports of patients getting re-infected with the new coronavirus,” Dr. Wilen says. “It is also known that for many seasonal coronaviruses which cause the common cold, the antibodies go away over time which enables people to get re-infected.”
The World Health Organization addressed this issue at a news briefing in Geneva on April 13.
"One would expect that a person who generates a full-blown immune response with detectable antibodies should have protection for a period of time," Dr. Mike Ryan, executive director of WHO's emergencies programs, said, per NPR. "We just don't know what that period of time is. We would expect that to be a reasonable period of protection, but it is very difficult to say that with a new virus."
Dr. Wilen suspects that even if the new coronavirus antibodies went away, that past infection would confer a survival advantage to future re-infection. “This is a general principle of the adaptive immune system,” he explains.
Is Testing Available—and What Does It Involve?
The Food and Drug Administration (FDA) recently approved the first test in the US for detecting coronavirus antibodies, and many companies are developing other tests.
Meanwhile, the Centers for Disease Control and Prevention (CDC) has already started carrying out its own antibody testing to help determine how many people have been infected with the virus, including those who never displayed any symptoms, reported Politico. On April 10, the National Institutes of Health announced that it would test 10,000 healthy volunteers from around the country for the presence of antibodies. People can participate in at-home blood sampling using a kit and mail the sample to the NIH lab for analysis.
Typically, the test involves taking blood from the arm or using the finger stick method, in which the finger is pricked with a lancet to obtain a small quantity of capillary blood. “The amount of blood needed depends on the specific test method,” Dr. Wilen says. Either way, it should be quick and simple.
How Reliable Are Antibody Test Results?
In other parts of the world, some governments have expressed concern that antibody tests are not proving to be as reliable as the swab tests that look for current infection. On April 8, the UK government announced that antibody tests won’t be available until at least May because none of the tests tried so far had been accurate enough.
It’s crucial that the coronavirus antibody testing process isn’t rushed, Gary W. Procop, MD, the chair of American Society for Clinical Pathology’s Commission on Science, Technology and Policy, and vice chair and director of virology at Cleveland Clinic, tells Health. If the tests aren’t sensitive or specific enough, it could result in false positives, which suggest a person has immunity who doesn’t, and false negatives, which fail to detect immunity.
“Both of these are dangerous and hamper the efforts to get Americans safely back to work,” Dr. Procop says. “We need to follow the lead of our colleagues in the UK and not implement tests that have not been thoroughly vetted and may do more harm than good.”
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
Whether you have the virus or not, this development in the fight against COVID-19 affects everybody—wide-scale antibody testing may be key to getting those stay-at-home orders lifted.
What Is Antibody Testing?
Antibodies are human proteins produced by the body to fight infection. “During an infection, the immune system custom-designs antibodies to recognize a specific part of the virus,” Craig Wilen, MD, an assistant professor in laboratory medicine and immunobiology at Yale University, tells Health.
In the case of the new coronavirus, the most important antibodies target the viral spike protein, which is the protein that binds to the human cell receptor and allows the genetic material of the virus to enter human cells and begin infection. “There are two types of virus-specific antibodies that are relevant for testing,” Dr. Wilen says. “The first is called immunoglobulin M (IgM). This antibody is made earlier in the period of infection and then goes away. The second is called immunoglobulin G (IgG), which is made after IgM, but lasts much longer.”
While there is some variability in timing between people, IgM lasts for weeks to months and is detectable after a week or two, whereas IgG lasts for decades and is detectable days to about one week after IgM. By detecting the different antibodies in a person’s blood, doctors are able to “date” when they had—or still have—the infection.
If My Test Comes Back Positive, Am I Immune?
Unfortunately, scientists don’t yet know whether a positive test means you’re immune or how long such protection may last. “There have been reports of patients getting re-infected with the new coronavirus,” Dr. Wilen says. “It is also known that for many seasonal coronaviruses which cause the common cold, the antibodies go away over time which enables people to get re-infected.”
The World Health Organization addressed this issue at a news briefing in Geneva on April 13.
"One would expect that a person who generates a full-blown immune response with detectable antibodies should have protection for a period of time," Dr. Mike Ryan, executive director of WHO's emergencies programs, said, per NPR. "We just don't know what that period of time is. We would expect that to be a reasonable period of protection, but it is very difficult to say that with a new virus."
Dr. Wilen suspects that even if the new coronavirus antibodies went away, that past infection would confer a survival advantage to future re-infection. “This is a general principle of the adaptive immune system,” he explains.
Is Testing Available—and What Does It Involve?
The Food and Drug Administration (FDA) recently approved the first test in the US for detecting coronavirus antibodies, and many companies are developing other tests.
Meanwhile, the Centers for Disease Control and Prevention (CDC) has already started carrying out its own antibody testing to help determine how many people have been infected with the virus, including those who never displayed any symptoms, reported Politico. On April 10, the National Institutes of Health announced that it would test 10,000 healthy volunteers from around the country for the presence of antibodies. People can participate in at-home blood sampling using a kit and mail the sample to the NIH lab for analysis.
Typically, the test involves taking blood from the arm or using the finger stick method, in which the finger is pricked with a lancet to obtain a small quantity of capillary blood. “The amount of blood needed depends on the specific test method,” Dr. Wilen says. Either way, it should be quick and simple.
How Reliable Are Antibody Test Results?
In other parts of the world, some governments have expressed concern that antibody tests are not proving to be as reliable as the swab tests that look for current infection. On April 8, the UK government announced that antibody tests won’t be available until at least May because none of the tests tried so far had been accurate enough.
It’s crucial that the coronavirus antibody testing process isn’t rushed, Gary W. Procop, MD, the chair of American Society for Clinical Pathology’s Commission on Science, Technology and Policy, and vice chair and director of virology at Cleveland Clinic, tells Health. If the tests aren’t sensitive or specific enough, it could result in false positives, which suggest a person has immunity who doesn’t, and false negatives, which fail to detect immunity.
“Both of these are dangerous and hamper the efforts to get Americans safely back to work,” Dr. Procop says. “We need to follow the lead of our colleagues in the UK and not implement tests that have not been thoroughly vetted and may do more harm than good.”
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
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