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COVID-19 tests: diagnostic vs. antibody

Posted September 21, 2020 by Charles A. Zonfa, MD, FACOG | Chief Medical Officer and Vice President, Network Development and Contracting

As we wage war against COVID-19, testing is a powerful weapon to help stop the spread of the virus. 

Testing can be used to expedite care when needed and potentially identify individuals who require self-isolation. In addition, people they’ve come into contact with can be traced sooner, so those at risk can quarantine and watch for symptoms. 

Testing also helps epidemiologists determine how widely the illness has spread; it makes the “enemy” visible. 

Today, there are two types of COVID-19 tests available: diagnostic and antibody tests. Both serve the purpose to help stop the spread, but it’s important to differentiate between the two and know which one to take based on your circumstances. 

The COVID-19 diagnostic test determines whether you have an active coronavirus infection. Following the Centers for Disease Control and Prevention guidelines, this test may be appropriate if you think you’ve been exposed or are exhibiting symptoms. 

In contrast, the COVID-19 antibody test determines whether you had COVID-19 in the past and now your body has antibodies to help protect against future infection. Antibodies are produced by your immune system that are critical for fighting the virus and can take several days or weeks to develop after you had the infection. This test really only offers insight into exposure, so many medical professionals do not recommend it.

SummaCare gets to the bottom of what you need to know about diagnostic tests versus antibody tests. 

COVID-19 diagnostic tests

Currently, there are two FDA-approved tests to diagnose a COVID-19 infection:

PCR test: This test detects genetic material of COVID-19 using a lab technique called polymerase chain reaction, or PCR. It’s the most common and recommended test being used today. Fluid is collected either through saliva, or a swab from the back of the nose and throat. PCR tests can be very accurate when properly performed by a medical professional.
• Antigen test: This test detects certain proteins that are found on the virus’ surface. Fluid is collected through a nasal or throat swab. These tests are faster and less expensive, however, there’s an increased chance of a false-negative. This means it’s possible to be infected with COVID-19, but have a negative test result. There is also a risk of false positives. The U.S. Food and Drug Administration (FDA) has only approved a few of the available tests currently on the market.

It’s important to understand these tests are not 100 percent accurate. It is possible to get a negative result and still be infected with COVID-19. That’s why even if you receive a negative result, but you have symptoms or have been around someone infected, it’s still important to self-quarantine until symptoms subside. 

COVID-19 antibody test

Antibody testing is normally done after a person has fully recovered from COVID-19. A blood sample, either through a finger prick or drawing blood, is used to determine if you have developed antibodies against the virus. The American Red Cross also is conducting some antibody testing on donor blood to see if those donors can give convalescent plasma.

If your antibody test is positive and shows you do indeed have antibodies, it doesn’t necessarily mean you’re protected against reinfection. Not much is known about immunity to COVID-19, so be sure to continue to follow the recommended precautions.

It’s important to note the timing and type of antibody test affect accuracy. If you take the test too early and your immune system is still building up an immune response, the test may not detect antibodies. In addition, the FDA has only authorized certain antibody tests, but there are other questionable tests available today. 

Frequent hand washing, wearing a mask and social distancing are our first line of defense to help stop the spread. However, if you believe you’re currently suffering from COVID-19 or think you had it in the past, testing is another important defense to assist in the fight. 

If you’d like to get tested, call your physician to discuss your current situation to determine the best course of action. Don’t travel to a medical facility until you are instructed to do so. Be aware, however, access and eligibility to these tests may be limited in your area. 


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