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Nov 23

[ARCHIVED] Antigen (Rapid) Test for COVID-19 Explained

The original item was published from November 23, 2020 3:11 PM to November 23, 2020 3:13 PM

The ongoing COVID-19 pandemic requires testing in order to identify who is infected and prevent the further spread of the disease in our community. There are currently several testing methods to detect the virus that causes COVID-19 and many people have wondered which tests are best and which tests they should seek. 

In particular, many have asked about the value of the so-called “rapid” test that is designed to quickly diagnose a case of COVID-19. The rapid test is also called an antigen test. The antigen test provides results in approximately 15 minutes. It is also easy to run and affordable to administer. So, why isn’t the rapid test recommended more frequently? The answer is simple: the rapid COVID-19 test is not as accurate as the more widely available polymerase chain reaction (PCR) test, also called a molecular test.

What is a COVID-19 antigen test?

Like the PCR test, a COVID-19 antigen test is a type of viral test. A viral test tells you if you have a current infection by looking for parts of the virus itself through a swab of the back of the nose, mouth or throat. The antigen test looks for a specific protein on the surface of the virus while the PCR test looks for the virus’ genetic material. 

The sensitivity and specificity levels of antigen and PCR tests are different. Consequently, the U.S Food and Drug Administration (FDA) says the risk of false positive and false negative results is higher with an antigen test than with a PCR test. 

In May of 2020, the Loudoun County COVID-19 Testing Task Force identified a concern regarding the risk of false positive results from antigen tests and also cautioned that false positive results do not infer that a patient has any type of immunity to COVID-19.

At this time, utilization of antigen testing may be beneficial in circumstances where an early indication would prove useful and where PCR testing would be utilized for confirmation purposes, such as those discussed below in the next section.

What type of test should I get? 

The type of test you should get depends on your specific circumstances and should be discussed with your health care provider. In general, the Loudoun County Health Department recommends the PCR test when available and possible, which is considered the “gold standard.” 

Antigen tests could be considered in situations where PCR tests are not available or are subject to prolonged or excessive turnaround times. An example might be for symptomatic and asymptomatic residents and staff in congregate settings, such as nursing homes, where rapid turnaround times for disease screening is critical. Rapid tests generally should augment other testing efforts, such as a confirmatory PCR test.

In other instances, such as when an individual is traveling and requires proof of a very recent negative COVID-19 test, the rapid test can be useful if accepted by authorities in your travel destination. Generally, public health experts recommend the PCR test because it is more accurate. Additionally, the PCR test may be the only accepted type of test.  If you must travel, your trip planning should include sufficient time for you to obtain the PCR test. Labs can often provide PCR test results within 48 hours. 

Is a COVID-19 antigen test different from a COVID-19 antibody test?

Yes. An antibody test tells you if you had a past infection by looking for antibodies in the blood. Antibodies are proteins made by an infected person’s immune system when a germ enters the person’s body. The antibody test uses a blood sample to look for antibodies made in response to a COVID-19 infection; it does not detect the virus itself. It usually takes one to three weeks for the body to make antibodies in response to an infection. We do not know how much protection COVID-19 antibodies might provide or how long this protection might last. 

When should I get tested for COVID-19? 

You should get tested for COVID-19 if:
If you have COVID-19 symptoms, you may use Virginia’s COVIDCHECK to help make decisions on when to seek testing and appropriate medical care. It’s also a good idea to contact your health care provide for guidance. Always seek emergency medical care immediately if you are having trouble breathing, persistent pain or pressure in the chest, new confusion, inability to wake or stay awake, or bluish lips or face.

How can I get tested?

Contact your health care provider if you have symptoms or have had close contact with someone with COVID-19 and therefore should be tested for COVID-19. Testing may be available at your doctor’s office, urgent care center, pharmacy or other health care clinic. 

To find a testing site nearby, visit the Virginia COVID-19 Testing Sites website. Each testing site has different policies and procedures for testing and billing. Contact the COVID-19 testing provider to receive more information.

If you are specifically seeking a rapid test, look for providers near you. As of November 23, 2020, the following providers located in Loudoun County offer a rapid test for COVID-19 (Note: please contact the provider before visiting the location to confirm the availability and type of testing):
Does the Loudoun County Health Department offer rapid COVID-19 testing?

No. Loudoun County does not offer rapid COVID-19 testing. The county has organized community testing events, which have used the PCR test. Any future testing events will be announced on the county’s website, loudoun.gov 

If you have questions about testing or need help finding testing, call the Health Department information line at 703-737-8300, Monday-Sunday 9:00 a.m. to 5:00 p.m. or send an email

Learn More About COVID-19 Symptoms and Testing
Stay Informed
Loudoun County encourages residents to stay informed about about the impact COVID-19 has on our community.
  • Visit loudoun.gov/coronavirus for more information about how to protect yourself and your family and to sign up for email and text updates on COVID-19.
  • Opt in to receive text messages:
    • English: Text LCCOVID19 to 888777
    • Spanish: Text LCCOVIDESP to 88877
Residents with questions about COVID-19 may call the Loudoun County Health Department’s information line, 703-737-8300, or send an email.   

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