Antibody Testing for COVID-19: What You Need to Know

By Alana Smart / May 8, 2020 / Blog ,

Vial reading "COVID-19 antibody"

Antibody Testing for COVID-19: What You Need to Know


 *Please note the content of this article was up to date as of 5/7/2020

The race to gain an accurate understanding of the number of people who have been exposed to SARS-CoV-2 (the virus that causes COVID-19 disease) is on. Reasons for grasping the true spread of the virus are numerous. Epidemiologists want to understand the burden of the disease in different populations, politicians need to create policies and budget decisions based on accurate data, and employers are interested in keeping their employees healthy. One method of identifying those who have been exposed is through antibody testing. 

Antibodies and Antibody Tests

To understand what an antibody test is, we need to revisit Biology 101. Antibodies, also called immunoglobulins, are Y-shaped proteins generated by B lymphocytes (a type of white blood cell) in response to antigens. Antigensare substances that trigger immune responses and include viruses, bacteria, and toxins. Antibodies circulate through our bodies as part of the adaptive immune system looking for the specific antigens they were made to find. While there are many classes of antibodies, the job of an antibody is to identify and bind to a specific protein on an antigenWhen antibodies bind to antigens, antigens are neutralized and/or are tagged for destruction by other parts of the immune system. These antibodies can take 1-3 weeksto develop, and will continue to circulate for some time after people recover, potentially extending defenses against the disease a little longer.

According to the CDC, an antibody blood test checks the blood for specific antibodies, and in regard to the current COVID-19 outbreak would, “show if you had previous infection with the virus.” The phrase serological test is also used to describe blood tests that look for antibodies. You may see different types of antibody tests labeled to identify IgG, IgA, and IgM antibodies. The Ig stands for immunoglobulin. IgM antibodies are typically the first on the scene of an immune response.  IgG antibodies are part of secondary immune responses and can remain in the body for a long time. IgA antibodies protect mucus membranes.

Antibody Tests Versus Viral Tests

Antibody tests are not the same as the nose or throat swabs healthcare professionals perform on those who have COVID-19 symptoms. Those swabs are specimens used in what are called viral tests which look for SARS-CoV-2 nucleic acid. The nucleic acids indicate the presence of the virus itself. Here is one very generalized and simple way to categorize the two tests: the viral test tells who is currently infected and the antibody test tells who has had an infection in the past.

It is possible for a person who tests positive for a viral test to be negative for an antibody test. Antibodies take around a week to develop, so an infected person might not be producing antibodies at the time they were tested. It is also possible for a person to test negative on the viral test but positive on the antibody test. This would indicate a passed infection and mean antibodies are in their system as a result.

Positive Test Versus Negative Test Results

The CDC explains what both positive and negative test results from an antibody test mean. A positive antibody test result means antibodies for SARS-CoV-2 or a closely related coronavirus are present in your system; your body had an immune response to the virus. A person may test positive if they were sick in the past, or if they were infected but asymptomatic. Keep in mind that a positive test result from an antibody test is NOT the same as a diagnosis. Those who both test positive and have COVID-19 symptoms need to contact their healthcare provider and have a viral test performed to confirm their disease status.

A negative antibody test result means antibodies for SARS-CoV-2 are not detectable. This may indicate a few things. A person who tests negative on the antibody test and has had no symptoms of COVID-19 has most likely never had a SARS-CoV-2 infection. However, some people may have COVID-19 and take a while to develop antibodies, thus producing a negative test result. It is also possible for a person who tests negative to have a current infection and no symptoms. Even with negative test results, those who get sick should contact a healthcare professional and have a viral test performed if directed. Just because someone has tested negative once, does not mean they cannot encounter the virus later or test positive for antibodies at a future date.

One thing to remember when considering positive and negative test results is the newness of these tests. Antibody tests exist for other diseases, but antibody tests for the novel coronavirus are just emerging. Normally, medical tests like these must be approved by the FDA. Currently, only a handful of companies are approved to perform these tests under theEmergency Use Authorization (EUA) umbrella. This means tests on the market, even those approved under EUA, did not go through the same rigorous review they might otherwise. False positives and negatives are possibilities. Results should be used with caution and not finality. When reading about different tests, you might see the terms sensitivity and specificity used. Sensitivity refers to the percentage of true positives identifiable by a test and specificity refers to the percentage of true negatives identifiable by a test. The higher the sensitivity and specificity, the better.

Passport Immunity

There is an idea floating around right now that those who have been infected with SARS-CoV-2, recover (if they had symptoms), and test positive on an antibody test should be given an immunity passport. This certificate of sorts would allow those people who test positive to go back to work, travel, and resume life as normal since they have developed “immunity” and are safe. Those who test negative still have the potential to get sick and spread disease. While the idea sounds good initially, it is flawed, especially when the lack of data to support such a notion is considered.

The World Health Organization says, “there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an “immunity passport” or “risk-free certificate.” The CDC reminds us that it is unknown if those who have been infected once have immunity against subsequent infections. It is also not known how long antibodies to SARS-CoV-2 last in our systems and what level of protection those lingering antibodies provide. Until we know more, or until a vaccine is developed, passport immunity does not seem like the most reliable solution on a large scale. Additionally, granting freedoms, like travel, to those with antibodies and limiting freedoms to those who do not because they stayed at home or followed social distancing guidelines may be viewed as unfair.

How Can Antibody Tests Be Used

Antibody tests can provide society with useful data about COVID-19. For example the CDC is currently conducting surveillance using antibody tests to research crucial questions like: Are people who have antibodies protected against future infections? Antibody tests can help scientists gain a better understanding of the number of people who have been infected so they can paint a clearer picture of the COVID-19 impact on society. Doctors can use antibody information to understand their patients’ medical histories. Companies are even considering testing their employees.

The usefulness of antibody testing for employees may vary by industry. Offering antibody testing to employees, especially those who work in medical and service industries, may provide peace of mind. Many in these industries were not able to stay at home because of their jobs and they may be curious if they were ever infected. If researchers discover that antibodies do offer some protection against subsequent infections, those who have tested positive for SARS-CoV-2 antibodies may be able to continue working if there is a second wave of COVID-19 later. For example, if you have two doctors and one has the antibodies and the other does not, the doctor who has the antibodies can be assigned to work with COVID-19 patients first. The doctor who does not have the antibodies would then be protected from the possibility of a respiratory infection. If he or she were to get infected, he or she could act as a vector for the disease. Of course, with the limited knowledge we have, it is far too early to make those types of decisions and be confident we are doing the best thing for everyone. Staying up to date with research and acting accordingly will be the best option. The value and application of antibody testing will grow as more is learned about the disease.

Testing might also be conducted to help employers gauge if the social distancing, sanitizing, PPE, and other preventative measures instituted have been effective in limiting the spread of COVID-19 in the workplace. A company with a low percentage of people with antibodies might think their efforts were effective at slowing the spread of disease and decide to continue enforcing policies since a large chunk of employees would still be susceptible. 

Voluntary health screenings are common parts of corporate wellness programs. Companies can use antibody testing as part of a campaign targeted at educating employees on new health and safety policies being instituted in a post stay-at-home-order work environment. With all the attention COVID-19 has received, people will want to know if they were exposed or not. Providing voluntary testing may help employees know the company is serious about their employees’ health. Employees in return may understand the importance of staying home when they are sick (with anything, not just COVID-19).

If an employer chooses to mandate antibody testing, they should be able to explain their decision to their employees. Is testing necessary? Will knowing if an employee has been exposed to the SARS-CoV-2 virus provide any benefit?  What will you do with information gained? Will those who do not have antibodies be discriminated against? Employers who require any type of testing need to be familiar with the legality of medical screenings. All personal information must be kept secure in accordance with HIPAA laws. ADA, OSHA, and other applicable laws will need to be considered as well.

Antibody testing is a new and exciting development in this COVID-19 world. It has the power to tell us who has had an immune response! As we learn more about COVID-19, the power and applicability of that information will continue to grow. Hopefully, we will learn that people are protected from subsequent infections if they have had an immune response to the virus once. 

Is NMS Health Offering Antibody Testing?

NMS Health is not currently offering Antibody Testing to our clients until more data becomes available. Though the strides made on Antibody Testing have been impressive thus far, we feel there is not enough data to base hiring and business decisions off of these results. We are re-evaluating this offering on a weekly basis and will begin to offer Antibody Testing once we feel our clients can safely use the results of these tests.  Below you'll find some of the criteria we're evaluating before offering Antibody Testing to our clients:

  • A decrease in non FDA approved Antibody Testing tests throughout the market
  • An overall decrease in false positives and false negatives in terms of test results
  • A greater understanding reached by the scientific community on whether or not a positive antibody response means protection from reinfection

About NMS Health

NMS Health is an occupational health screening platform that can help you complete testing for your employees or candidates, anywhere in the country. If you’d like to learn more about how we simplify the health screening process and save our clients time and resources, check out an overview of our services here.

This article was written by Alexandra Cox

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