COVID Testing Explained By: Mary Ellen Pratt, FACHE, CEO
Testing is vital in our nation’s response to COVID-19. Through the pandemic, the U.S. Food and Drug Administration (FDA) has issued EUAs—Emergency Use Authorizations—for different types of COVID-19 testing. Diagnostic Testing—typically done through a swabbing of the nose or throat, can confirm an active infection and is typically done for symptomatic patients. Antibody (serological) testing checks the blood for antibodies that are created by the immune system when a virus is introduced. This blood test can be useful for asymptomatic patients who are concerned about an exposure to COVID-19. Antibody Tests are NOT intended to diagnose an active infection.
The two methods of COVID-19 Diagnostic Tests approved by the FDA include Molecular and Antigen Tests. Molecular Tests, such as polymerase chain reaction (PCR) tests, can detect genetic information in the virus’ RNA. Antigen Tests detect specific proteins on the surface of the virus. Before being authorized, all COVID-19 tests are evaluated based on their sensitivity (ability to detect those positive for the virus) and specificity (ability to detect those negative for the virus). Sensitivity and specificity vary for different testing methods.
Each category of diagnostic test has its own unique role in the fight against the Coronavirus, but it is important to understand the differences between both the tests and their results.
Lab-based Molecular Testing
According to the FDA, “PCR tests can be incredibly accurate, but running the tests and analyzing the results can take time.” Lab-based molecular testing—like those used at St. James Parish Hospital—can take between 24 hours (state tests) and up to a week (commercial tests) to be confirmed. These tests are sent off to be analyzed by highly trained, licensed professionals utilizing state-of-the-art laboratory equipment. Though results are not instant, these tests are both highly sensitive and specific—meaning positive AND negative results are confirmed.
Antigen testing was designed for rapid detection of COVID-19. “One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes. However, antigen tests may not detect all active infections, as they do not work the same way as a PCR test. Antigen tests are very specific for the virus, but are not as sensitive as molecular PCR tests,” reports the FDA.
According to the FDA, positive results from antigen tests are highly accurate; however, they have a higher chance of producing false negative results. Therefore, negative results do not rule out an infection.
Point-of-Care, Rapid Testing
Both molecular and antigen testing methods can be completed on-site at clinics, physicians’ offices and hospitals in an effort to produce results quickly. Through relaxed regulations, point-of-care, rapid testing can often be administered by any health care provider. The FDA has cautioned the public to understand that point-of-care antigen tests and some popular rapid, molecular tests must be used with the understanding that there is a higher chance of a false negative result.
The Pros and Cons—not all results are created equal
Lab-based molecular tests take longer to result due to the hands-on method of analysis. Results are not instant, but are “highly accurate” and according to the FDA do not need to be repeated. If you get a positive or negative result from a lab-based test like those currently administered through the hospital and its clinics, you can trust that result.
Antigen and/or other forms of rapid, point-of care tests conveniently offer results within minutes. Positive results are very accurate, but the FDA considers negative results “presumptive” and further states that if a negative result is “inconsistent with clinical signs and symptoms or necessary for patient management, patients should be tested with different authorized or cleared molecular tests.”
Accuracy of any COVID-19 test will be higher if you wait until you are symptomatic to be tested. If you’ve been exposed to someone with the virus, but are not showing symptoms—recommendations have not changed. Social distancing is still key—stay home, self-isolate yourself, wear a mask and contact your physician as soon as you notice any new symptoms.
If you recently tested negative through a rapid, point-of-care COVID-19 test, talk to your provider about getting the test confirmed through a molecular test especially if you begin to notice new or worsening symptoms.
Visit www.sjph.org/coronavirus often to learn about new testing information and COVID-19 announcements.
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