COVID-19 Testing: Understanding the Difference
We must work together to stop or slow the spread of the coronavirus.
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There is an abundance of information circulating in the news and on social media about coronavirus (COVID-19) testing. It’s not surprising that there’s confusion about tests and how they differ.
“To say there’s complexity and confusion around testing for COVID-19 is an understatement,” said Dr. Dean Watson, Vice President and Chief Integration Officer at Tallahassee Memorial HealthCare (TMH). “For starters, COVID-19 is the disease caused by the SARS-CoV-2 virus. All of the tests we use to assist in the diagnosis of COVID-19 are looking for signs that the person has been infected with SARS-CoV-2 virus.”
There are three main categories of tests for the SARS-CoV-2 virus: molecular tests, antigen tests and antibody tests. Of these, the molecular and antigen tests are used to diagnose COVID-19. Antibody testing, also known as serology testing, is done after full recovery from COVID-19.
- Molecular test. Also called a polymerase chain reaction (PCR) test, this test detects genetic material of the virus and can diagnose active coronavirus infection. A healthcare provider collects fluid from a nasal or throat swab or from saliva. Depending on your location, results may be available in minutes (some locations) if analyzed onsite or up to a week if sent to an outside lab. This test is typically highly accurate and usually does not need to be repeated. This test detects if a person currently has COVID-19, it cannot detect if a person had COVID-19 in the past.
- Antigen test. This rapid diagnostic test detects certain proteins that are part of the virus. Using a nasal or throat swab to get a fluid sample, antigen tests can produce results in one hour or less. Positive results are usually highly accurate, but there's an increased chance of false negative results — meaning it's possible to be infected with the virus but have negative antigen test results. Because an antigen test isn’t as sensitive as a molecular test, your healthcare provider may order a molecular test if you test negative but have symptoms of COVID-19.
- Antibody test. A healthcare provider takes a blood sample, usually by finger stick, to determine if you’ve developed antibodies against the virus. Antibodies (or proteins) are produced by the immune system and are critical for fighting and clearing the virus. There are two types of antibody tests available: IgM and IgG. IgM can aid in determining if someone is acutely ill, but it is not dependable, according to Dr. Watson. The IgG test is the chronic or post-acute test that shows if you have antibodies, indicating that you were likely exposed to COVID-19 at some point in the past. Results can be received in as few as one to three days. It is important to note that with even the most sensitive and specific antibody test, these tests cannot determine if a patient has protective immunity. Unfortunately, we don’t know enough about immunity with regards to COVID-19 yet. Early studies are promising – showing some level of antibody will likely provide protection from future exposure.
TMH only uses the PCR and IgG tests. “Results are usually available within a few hours at TMH and at other locations locally. LabCorp and Quest results usually come back in a few days,” said Dr. Watson.
Testing is an effective part of battling COVID-19. These tests can provide a better understanding of how and where the virus spreads and offer critical information on medical care for individuals. However, it’s important to note that no COVID-19 test is 100% accurate.
“The most important message is to remain vigilant with protective measures like wearing masks and face coverings, distancing six feet apart and frequent hand washing. These safety measures are necessary to protect our communities and each other from the virus,” noted Dr. Watson.