TWO Basic Types of COVID-19 Tests
Since the Centers for Disease Control and Prevention (CDC) confirmed the first case of COVID-19 in the US on February 26, every state in our country continues to report new cases of people infected with the novel coronavirus (SARS-CoV-2). Even after more than a month in quarantine, SARS-CoV-2 testing continues to be a hot topic of discussion as states struggle to ramp-up testing availability. There are (2) main types of SARS-CoV-2 tests currently available:
- Testing for the presence of virus itself. These require a nasal swab. These diagnose an active COVID-19 infection were the patient is contagious.
- Testing to detect antibodies to COVID-19. These tests require a blood sample - finger prick or standard blood draw. The antibody test identifies individuals who have developed an immune response to COVID-19.
Overview in this short video below. More details in article which follows.
Dr. Calendine Explains the Role COVID-19 Testing
Types of COVID-19 Tests Available
1. Tests for Active COVID-19 Illness
As pockets of COVID-19 emerged in communities throughout the US, the focus was initially on developing tests to detect if someone was actively infected with the novel SARS-CoV-2 virus. These tests are designed to detect the presence of virus in mucous and saliva. Due to limited availability, these tests were initially available only to those with the most severe COVID-19 symptoms (shortness of breath, high fever, severe cough). Even during the height of COVID-19 spread in the US, many patients with mild to moderate symptoms of COVID-19 illness were unable to obtain testing.
Here in Tennessee, we are just now seeing increased availability to testing for the virus. Weekend drive through centers - sponsored by with state under the direction of Governor Lee have increased access dramatically. - Cory Calendine MD
Several companies are now producing diagnostic COVID-19 tests that detect the presence of the SARS-CoV-2 virus in the body. These tests are increasingly available at hospitals, clinics and even some drive-thru testing centers. Tests designed to detect the presence of the SARS-CoV-2 virus are typically done by collecting respiratory samples with either a nasal or throat swab. Pandemic numbers of COVID-19 have created the need for rapid testing innovation with some “point-of-care” tests now capable of providing results within minutes (Abbott Laboratories isothermal nucleic acid amplification test). Most recently (April 21, 2020), the U.S. Food and Drug Administration in cooperation with Laboratory Corporation of America (LabCorp) authorized the first diagnostic test with a home collection option for COVID-19. So now,without leaving home, patients can be provided a home collection kit including nasal swabs which is then returned LabCorp to complete testing for presence of the SARS-CoV-2 virus.
The limitation of "virus detection" tests is that they are only useful when there is coronavirus material present in mucous or saliva. Once a person is infected with a virus (including the SARS-CoV-2 virus), a person’s body will mount an immune response to fight the virus and will eventually clear any presence of the virus from the body. Some studies suggest that during an acute COVID-19 infection, the SAR-CoV-2 virus remains detectable in the throat for less than a week and may clear from nasal mucous in less than 2 weeks. After the body's immune system has responded to an active COVID-19 infection, tests that rely on detecting the SARS-CoV-2 virus in mucous or saliva are no longer useful. Therefore AFTER a patient has recovered from COVID-19, testing is based on detecting "antibodies" (not virus) in the patient's blood (antibodies are part of the body's response to the virus). Antibodies will remain in the body a long period of time after the SARS-CoV-2 virus has cleared from the body.
2. COVID-19 Antibody (Serologic) Tests
Unlike tests designed to diagnose an active COVID-19 infection, antibody (or serologic) tests can help identify individuals who have recovered from (or developed an immune response) to the SARS-CoV-2 virus. Part of the body’s immune response to any viral infection is the production of antibodies including IgM and IgG ( the body produces unique IgM and IgG antibodies to fight the infection). According to the FDA, IgM antibodies to SARS-CoV-2 are generally detectable in the blood several days after catching the virus, although levels over the course of infection are not yet well established. IgG antibodies to SARS-CoV-2 generally become detectable in the blood 10–14 days after infection and normally peak around 28 days after the onset of COVID-19 symptoms. Even if an individual has mild or no symptoms during a COVID-19 infection, antibodies are expected to still be detectable in the blood following the infection. Testing for antibody presence in the blood can help us determine who has had the virus and the percentage of our population that has had COVID-19 disease. A positive antibody test may also indicate some future immunity to SARS-CoV-2, although it is not yet clear how long or how effective this immune response "protection" lasts after a COVID-19 infection.
As cities are beginning to lift quarantine restrictions, and people are eager to return to work - it is now more useful to identify individuals who may already have some immunity to the SARS-CoV-2 virus. It is presumed that once a person has been infected with the SARS-CoV-2 virus (even if they only had mild or no symptoms), their chance of a recurrent infection during the subsequent 3 to 4 months is relatively low. This information would obviously be valuable to an individual returning to work or student returning to school. Unfortunately, the strength and duration of that protection is simply not yet known. The United States Food and Drug Administration approved the first US Antibody (serologic) test on April 2nd, and to date, has given emergency approval for (3) additional Antibody-based tests in the US. The accuracy of these tests remains uncertain and researchers warn that the percentage of COVID-19 survivors who are producing neutralizing antibodies is not yet well understood. There is still a great deal about COVID-19 immunity that we don’t yet fully understand. We do expect that data from more widespread testing will help us track the spread of the virus nationwide and assess the effectiveness of public health efforts to control COVID-19.
Unless we understand testing - all types, we run the risk of causing more confusion than good. Any one with question should reach out to us here at the Bone and Joint Institute or other trusted medical provider for more information. - Dr. Calendine
CNN's Dr. Sanjay Gupta walks us through his coronavirus antibody test
SAR-CoV-2 Antibody Testing is not yet available to the general public. However, since healthcare workers are regarded as high-risk, Dr. Sanjay Gupta, CNN correspondent and Emory University Surgeon, was recently able to provide an inside perspective as he received a SAR-CoV-2 antibody test at Emory University Medical Center in Atlanta. Dr. Gupta explains the COVID-19 Antibody testing process from the initial blood draw, centrifuge serum-separation in the lab, and combination of the serum with the SAR-CoV-2 virus to determine the presence of antibodies.
"If you have antibodies against the COVID-19 virus, they're going to combine, and we're going to be able to detect that (presence of the SAR-CoV-2 virus)."
Dr. Gupta explains that IgG antibodies appear in the body days after a COVID-19 infection has started and may provide immunity for a long time after. How long? How strong? That, we just do not know yet. According to Dr. Gupta and Dr. Roback, it is still too early to fully understand how much immunity or protection is provided by the COVID-19 antibodies that these tests are measuring. As Dr. Gupta explains, one thing that antibody tests do tell us is that,
"If you test positive for the antibodies, that means you've dealt with this infection (COVID-19), and you beat it. Chances are that if you're exposed to it again, you'll beat it again."
Check out the video above to find out Dr. Sanjay Gupta's Antibody test results. (Source: CNN.com)
SUMMARY: Why is COVID-19 Testing Important?
COVID-19 testing is playing a vital role in our nation emerging from quarantine. Rapid COVID-19 tests designed to diagnose an active infection are increasingly available at outpatient clinics, urgent care centers and emergency departments. Rapid identification of individuals that are carrying the SAR-SoV-2 virus will allow us to trace their close contacts and isolate those at higher-risk for COVID-19 infection. Meanwhile, antibody (serologic) tests will help identify people who have previously had a COVID-19 infection (even if they never developed symptoms) and therefore, may have some immunity to reinfection. Together, these categories of COVID-19 tests will help our country get back to work, back to school, and back to a more 'normal' level of social activity.
Additional COVID-19 Testing Resources:
- Centers for Disease Control and Prevention (CDC), https://www.cdc.gov/coronavirus/2019-ncov/lab/testing-laboratories.html
- US Food and Drug Association, https://www.fda.gov/medical-devices/emergency-situations-medical-devices/faqs-diagnostic-testing-sars-cov-2