COVID-19 and PCR Testing

Overview

What is a PCR test?

A polymerase chain reaction (PCR) test is performed to detect genetic material from a specific organism, such as a virus. The test detects the presence of a virus if you are infected at the time of the test. The test could also detect fragments of virus even after you are no longer infected.

What is a COVID-19 PCR test?

A PCR test for COVID-19 is a test used to diagnosis people who are currently infected with SARS-CoV-2, which is the coronavirus that causes COVID-19. The PCR test is the “gold standard” test for diagnosing COVID-19 because it’s the most accurate and reliable test.

Who should get tested for COVID-19?

Get tested:

  • If you have symptoms of COVID-19.
  • If you have been within six feet of someone for 15 minutes or more who has tested positive for Covid-19. (Note: some testing sites don’t offer testing if you’ve been exposed but don’t have symptoms.)

Test Details

How does a COVID-19 PCR test work?

There are three key steps to the COVID-19 PCR test: 1) sample collection, 2) extraction, and 3) PCR.

  1. Sample collection is done using a swab to collect respiratory material found in your nose. A swab contains a soft tip on a long, flexible stick that is inserted into your nose. There are different types of nose swabs including nasal swabs that collect a sample immediately inside your nostrils and nasopharyngeal swabs that go further into the nasal cavity for collection. Either type of swab is sufficient for collecting material for the COVID-19 PCR test. After collection, the swab is sealed in a tube and then sent to a laboratory.
  2. When a laboratory technologist receives the sample, they perform a process called extraction, which isolates genetic material from the sample including genetic material from any virus that may be present.
  3. The PCR step then uses special chemicals and a PCR machine, called a thermal cycler, which cause a reaction to occur that makes millions of copies of a small portion of the SARS-CoV-2 virus’s genetic material. During this process, one of the chemicals produces a fluorescent light if SARS-CoV-2 is present in the sample. This fluorescent light is a “signal” that is detected by the PCR machine and special software is used to interpret the signal as a positive test result.

Results and Follow-Up

What do COVID-19 PCR test results mean?

A positive test result means that it is very likely that you have COVID-19. Most people have mild illness and can recover safely at home without medical care. Contact your healthcare provider if your symptoms get worse or if you have questions or concerns.

A negative test result means you probably didn't have COVID-19 at the time you took your test. However, it is possible to be infected with SARS-CoV-2 but not have enough virus in your body to be detected by the test. For example, this may happen if you recently became infected but you don’t have symptoms, yet; or it could happen if you've had COVID-19 for more than a week before being tested. Keep in mind that a negative test doesn’t mean you are safe for any length of time. You can be exposed to COVID-19 after your test, get infected and spread the SARS-Cov-2 virus to others.

If your test is positive, talk with your healthcare provider, stay home and separate yourself from others. If your test is negative, continue to take steps to protect yourself and others from getting COVID-19. Read more about what to do if you test positive and ways to prevent getting infected with COVID-19.

How soon are results of a COVID-19 PCR test available?

You should receive the results of your test as early as 24 hours after sample collection, but sometime it can take a few days depending on long it takes the sample to reach the laboratory and how many other samples are in the queue to be tested.

What are the advantages of a COVID-19 PCR test?

The main advantages of COVID-19 PCR test are its accuracy and reliability. It is the most accurate test available for COVID-19 detection.

Are there downsides to a COVID-19 PCR test?

Because the test is able to detect very small amounts of virus material, it can continue to detect fragments of SARS-CoV-2 virus even after you’ve recovered from COVID-19 and are no longer contagious. So you may continue to test positive if you have had COVID-19 in the distant past, even though you can’t spread the SARS-CoV-2 virus to others.

Additional Details

How does the COVID-19 PCR test compare with other available COVID-19 tests?

Basically, there are two types of tests, diagnostic tests and antibody tests. Diagnostic tests tell you if you have an active (current) COVID-19 infection. Antibody tests tell you that you already had COVID-19.

Diagnostic tests:

  • PCR test: This tests for the presence of the actual virus’s genetic material or its fragments as it breaks down. This is the most reliable and accurate test for detecting active infection.
  • Antigen test: This test detects bits of proteins on the surface of the virus called antigens. Antigen tests are typically considered rapid, taking only 15 to 30 minutes but are less accurate than a PCR test. Rapid antigen tests are most accurate when used within a few days of the start of your symptoms, which is when the largest amount of virus is present in your body. Because this test is not as accurate as a PCR test, if an antigen test is negative, your healthcare provider may order a PCR test to confirm the negative test result.

Antibody test:

  • Antibody (serology) test: This tests detects if you’ve had an immune response (antibodies) to the virus. This means that you’ve had the virus and your body (immune system, specifically antibodies) has mounted an attack to fight it. The test is detecting those antibodies. It typically takes about a week after being infected for enough antibodies to develop to be detected in your blood. For this reason, this test shouldn’t be used to diagnose an active infection.

How do I find out where to get tested for COVID-19?

If you have symptoms of COVID-19 or have been exposed to people who have symptoms or have tested positive, you may want to be tested. First, talk with your healthcare provider. They will review your symptoms in person or on a video appointment. The provider will place an order for a test and tell you where you can be tested. Keep in mind that if you’ve been exposed to the SARS-CoV-2 virus but don’t have symptoms, call the testing site first to make sure they will allow you to be tested.

You can also call or check the websites of your local hospitals in your health insurance network or check with community health centers or urgent care centers. The U.S. Department of Health and Human Services provides links to find community-based testing sites in your state. You can also check your state or local health department websites for the latest information on testing locations. The Centers for Disease Control provides links to these state and local health departments.

Last reviewed by a Cleveland Clinic medical professional on 11/30/2020.

References

  • Centers for Disease Control and Prevention. Coronavirus Disease. . Accessed 11/25/2020.Testing (https://www.cdc.gov/coronavirus/2019-ncov/testing/index.html)
  • U.S. Food and Drug Administration. . Accessed 11/25/2020.Coronavirus Disease 2019 Testing Basics (https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics)
  • Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19). . Accessed 11/25/2020.Using Antigen tests (https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.htmhttps:/www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html#:~:text=Rapid%20antigen%20tests%20perform%20best,of%20COVID%2D19.l)
  • Floriano I, Silvinato A, Bernardo WM. . Rev Assoc Med Bras 2020 Jul;66(7):880-888. Accessed 11/25/2020.Accuracy of polymerase chain reaction (PCR) test in the diagnosis of acute respiratory syndrome due to coronavirus: A systematic review and meta-analysis (https://www.scielo.br/scielo.php?pid=S0104-42302020000700880&script=sci_arttext)

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