Photo by Mufid Majnun on Unsplash

From the Orange County Newsroom 

The U.S. Food and Drug Administration (FDA) has authorized three specific types of tests for diagnosing a COVID-19 infection, but they do not all work the same way, nor do they tell you the same information.

Here is what you need to know about each one.

Diagnostic Tests (aka PCR Test)

Diagnostic (molecular) tests detect the genetic material unique in COVID-19 using a lab technique such as polymerase chain reaction (PCR) or other techniques that amplify the virus in order to identify. Fluid is collected from a nasal or throat swab and is usually sent to an outside lab. PCR tests are highly sensitive and specific for diagnosing current infection. PCR tests are considered the most accurate and “gold standard” for diagnosing current infection.

PCR tests use a nasopharyngeal swab, which goes deep into your nose to the back of your throat. However, a few days may pass before the virus starts replicating in your throat and nose, so PCR tests will not identify someone who has recently been infected. Other things to note:

  • If you need to travel out of the country or for any other purpose, a molecular test is most likely required.
  • Lab results are needed and are usually sent back in approximately 48 hours (this varies depending on lab demand).

Antigen Test (aka Rapid Test)

Using a nasal or throat swab to get a fluid sample, health workers administer antigen tests to detect certain proteins in COVID-19. This test is often called a “rapid test” because the turnaround time is usually much quicker than a PCR test (it can produce results in about 15 minutes). Because of this, antigen tests are being used to screen large numbers of people and have been in high public demand.

Antigen tests are intended for symptomatic persons within 5-12 days of onset of symptoms.

While antigen tests are considered very specific, they are less sensitive then PCR.

An antigen test is more likely to miss active infection than a PCR test, so it is recommended you not only just rely on an antigen test if you have symptoms and/or have been at-risk for exposure to COVID-19. You should make sure to get both an antigen and a PCR test to ensure accuracy. Other things to consider:

  • Rapid tests do not detect false positives (unless something is wrong with the actual test), but if you do not show any symptoms, there is a chance the test can be false negative.
  • If you have COVID symptoms and you get back a negative antigen test, you still need a PCR test and should consider yourself to have COVID until the results of the PCR test are known.
  • At hospitals, they will most likely offer you a rapid test first. If you test positive, they will give you a PCR test to ensure accuracy.

Antibody Test (aka Serology Test or Blood Test)

The antibody test indicates if your immune system has produced antibodies to COVID-19, regardless of whether you ever showed symptoms. Locally, OneBlood is testing all blood donations for the COVID-19 antibody. These tests generally produce results in a few minutes based on a drop of blood taken from the finger. If you take a test too early—while your immune system is still mounting its defense—it may not provide an accurate result. The Mayo Clinic does not recommend antibody testing until at least 14 days after the start of symptoms.

  • Remember, even if you test positive for antibodies, it does not make you “immune” for a long period or indefinite amount of time … so you must still protect others who are not immune.

Free Testing Resources

Both molecular (PCR) and antigen (rapid) tests are now being administered at the Orange County Government Health Services testing site. For more information on this free testing site and which test may be the best choice for you, visit ocfl.net/Testing and click on #1 on the testing map.

2 COMMENTS

  1. In your comments about the PCR being the “gold standard” you left out information regarding current questions about its reliability without knowing the cycle threshold of the sample. As I understand it the lower number of times the test sample is cycled (replicated) to obtain a positive the higher the probability of having the virus, however the higher number of cycles the less reliable the test result is to the point that if is cycled over 40 times and a positive is obtained the test result is considered negative. So on December 3 Governor DeSantis, through the FDOH, ordered labs to include the cycle threshold number in their results reported to the state.

    • Thank you for the further details. This information was provided through Orange County as an overview on differences rather than a deep dive report. Hopefully this will be a starting point for understanding and further investigation rather than end as certainly this field and COVID-19 understanding continues to progress. Thank you again for sharing.

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