Public Health

Coronavirus Antibody vs. PCR vs. Rapid COVID Test - Which is Best?

Khang T. Vuong, MHA22 Dec 2020

Antibody vs PCR vs Rapid COVID Test - Which is Best?

Updated December 21st 2020 by Jacqueline Slobin, University of Virginia & Alyssa Orcuilo, The City University of New York

What types of COVID tests are available? 

There are currently two main tests for the COVID-19 virus in the United States - diagnostic tests and antibody tests. 

Diagnostic tests detect an active infection with COVID-19 and are either done through a nasal swab or a saliva sample. The two types of diagnostic tests are molecular PCR tests and antigen (rapid) tests. 

Antibody tests are done through a blood test to detect a previous infection with COVID-19. 

Comparison: what is the difference between a PCR test (nasal swab) and an antigen test for COVID-19? 

Both PCR and antigen tests are diagnostic tests; therefore, you should get either of these tests if you are experiencing symptoms of COVID-19. According to Harvard Health Publishing, there are a few key differences between the PCR test and antigen (rapid) test. We outline important differences in the table below:

PCR TestAntigen (rapid) Test
Nasal/throat swab or saliva sampleNasal swab
Results can take up to a week Results in less than one hour
Lower chance of false negative resultsHigher chance of false negative results 
Works by directly detecting the presence of the virus genetic material (RNA)Directly detects molecules on the surface of the virus

The bottom line: antigen tests produce results faster, but have a higher chance of yielding false negative results. Your doctor may want to get a PCR test to confirm a negative test result from an antigen test. 

What is the PCR test? And how does it work?

What is it? 

RT-PCR, or real-time polymerase chain reaction, is used to detect an active infection of COVID-19. Samples for a PCR test can be taken through a nasopharyngeal swab or a saliva test. 

What are the differences between the nasal swab and saliva PCR tests?

The saliva sample is a less invasive test than taking a nasopharyngeal sample. Like the nasal swab, the saliva test detects active COVID-19 infection in patients who are experiencing symptoms or who may have been exposed to someone with coronavirus

While the saliva tests are less commonly used than nasal swabs, the accuracy of the tests is very similar. 

How does it work?  

The RT-PCR technique targets a specific segment of the genetic material of the virus to detect the presence of COVID-19. RT-PCR works by making thousands of copies of this genetic material to qualitatively assess if the virus is present. The test only detects the virus while the person is currently infected. 

Timeline, Accuracy, and Important Information 

It is important to know that your PCR may yield a false negative result, meaning you are infected with the active coronavirus but your test result comes back negative. False-negative results may be caused by taking the sample incorrectly or getting tested too soon after exposure. This means that if your swab test comes back negative, you cannot certainly rule out the chance of having COVID-19.

If you get a PCR test the day you were exposed to someone with COVID-19,  the likelihood of receiving a false-negative test result is 100%. For the most accurate results, healthcare professionals recommend getting tested about 7 days after exposure or about 3-4 days after symptom onset. Consult your provider for more details on the accuracy of the specific test they are using. 

PCR tests can take several days (typically around 5 days) to process. Some rapid tests use PCR and can yield results within a few hours. For example, the Abbott ID Now test is a PCR rapid test that is FDA approved. 

Are there at-home PCR tests? 

9 companies currently produce at-home PCR tests. You complete the nasal swab at-home and mail in your sample to a lab. For more information on at-home PCR tests, see our article. 

What is the rapid antigen test? And how does it work?

What is it? 

Some urgent care facilities, testing centers, and doctors' offices are offering a rapid antigen test to diagnose a current infection with COVID-19. Rapid tests may be useful for individuals who need to return to work as soon as possible and cannot wait for the results of a PCR test.

How does it work?  

The antigen test works by detecting specific molecules on the surface of the virus. This is the same way that rapid strep throat tests are completed. 

Timeline and Important Information 

Patients are typically able to get the results of a rapid COVID test in as quickly as 15 minutes. Rapid tests are not available at as many locations as standard PCR tests, so make sure to call in advance to make sure this test is available. Additionally, rapid tests may be more expensive and require out of pocket costs.

Are Rapid Tests Accurate?

It is important to note that rapid antigen tests are less accurate than PCR tests; thus they are more likely to yield a false negative result. For this reason, antigen tests are not sufficient for travel to many states in the U.S.  Make sure to consult with your provider regarding the accuracy of the specific antigen test used.

Are there at-home rapid tests?

The FDA recently authorized an at-home, over the counter rapid test: The Ellume COVID-19 Home Test. This test is completed by taking a nasal swab and stirring it in a solution. You can get results sent to your phone in only 20 minutes. It is expected that this test will cost about $30. 

What is the antibody blood test? And how does it work? 

What is it? 

This test checks to see if individuals have been previously infected with the COVID-19 virus by looking for a specific antibody in the bloodstream. Antibodies are small proteins that are part of our immune system. They are produced to defend our body against a specific virus, for example, COVID-19.

The blood test looks for the specific antibodies that fight infection from the coronavirus. According to the Centers for Disease Control, it normally takes one to two weeks after someone becomes sick with COVID-19 for their body to make antibodies. Others may take even longer to develop antibodies to prevent future coronavirus infection. 

How does it work?  

The test checks to see if we have the antibodies for COVID-19. Antibody levels are detected through a test called ELISA, or serological enzyme-linked immunosorbent assay, and ultimately tests for the number of antibodies in the blood for the specific virus.

The test tells us if we already had the virus, but it is not currently being used for quick detection like the PCR and antigen tests. Antibody tests can detect the virus even after the patient has recovered.

Timeline, Accuracy, and Important Information 

Blood test results are typically available within 1-2 days. The antibody test has 2 major implications. First, the test can be used to identify potential blood donors in individuals who recovered from COVID. Blood from COVID-19 survivors can possibly be used to treat current COVID-19 patients. Second, the antibody blood test may give us insight into how long the antibodies last after infection with COVID-19. 

Note: testing positive for the COVID-19 antibody test means you have previously been exposed to the virus but does not necessarily confer immunity. For more details on the antibody test, what the results mean, and when to get one, see our article.

Which COVID test should I get - should I get a rapid test or PCR? 

In general, PCR tests are more accurate than rapid tests. Therefore, if you can wait about 5-7 days for your results, you should get the PCR test. If you need results immediately, you should get a rapid test. In addition, rapid tests are not qualified for travel to most states with restrictions. You must get a PCR test within 72 hours of travel if going to a state with a travel restriction. 

This chart will give you a comprehensive breakdown of which coronavirus test you should get in different scenarios: 

pcr vs rapid covid test - when to get each test

Where can I get tested for COVID-19? 

Testing protocols, regulations, and locations continue to vary by city during the coronavirus outbreak. If you are experiencing symptoms of COVID-19, you should seek medical attention and inquire about getting a test. See the links below for information on testing near you: 

For a comprehensive guide to testing sites in New York City, see our article here.

Healthcare could be confusing - here are other COVID-19 resources for you:

References:

https://www.fda.gov/media/134922/download

https://www.scientificamerican.com/article/heres-how-coronavirus-tests-work-and-who-offers-them/

https://www.pacificimmunology.com/resources/antibody-introduction/what-is-an-antibody/

https://www.livescience.com/how-coronavirus-tests-work.html

https://www.the-scientist.com/news-opinion/first-saliva-test-for-covid-19-approved-for-emergency-use-by-fda-67416

https://www.health.harvard.edu/diseases-and-conditions/if-youve-been-exposed-to-the-coronavirus

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