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COVID-19 Testing: Understanding the Options

COVID-19 Testing: Understanding the Options

Learn how PCR, antigen and antibody tests differ and what the results mean.

Updated on May 21, 2020 at 3:00pm EST.

Testing for COVID-19 is central to informing public health about the scope of the pandemic, re-opening economies around the world and enabling people to resume their jobs and daily activities safely.

But it’s also a source of confusion for many people. There is more than one type of test for COVID-19, each type is performed differently and their results mean very different things.

Diagnosing and tracking COVID-19
When experts talk about testing for SARS-CoV-2, they’re really referring to two different categories: diagnostic tests and antibody tests.

Diagnostic tests are intended to reveal whether or not you’re currently infected. There are two types being used: a polymerase chain reaction (PCR) test and an antigen test. Both of these tests check for the coronavirus itself, using saliva or a respiratory sample collected by nasal or throat swab.

Using a six-inch swab, a healthcare provider will take the sample from your nose and the back of your throat. If you are coughing up mucus, that may be tested as well.

PCR tests look for evidence of genetic material from the virus. Antigen tests are designed to detect fragments of proteins found on or inside the virus.

PCR tests are typically more accurate than antigen tests but take longer—hours or days—to process. Antigen tests, on the other hand, can provide results within minutes. Although positive antigen test results are very reliable, these tests tend to miss more cases than PCR tests. So, a negative antigen test result may need to be confirmed with a PCR test.  

Understanding the scope of the pandemic
Unlike these two types of diagnostic tests, an antibody test doesn’t tell you if you have the disease right now. Rather, it helps determine if you’ve ever been infected.

Why is this helpful? In general, large-scale antibody testing helps epidemiologists—the scientists who track disease outbreaks—estimate the size and spread of a pandemic, as well as zero in on groups who are at higher risk.

For the current pandemic, we also need to know who’s already been exposed to the novel coronavirus and recovered, including silent spreaders—those who may not have been tested or may not have even shown symptoms while they were infected. This information will likely play an important role in getting people, especially health care workers, back to work.

Rather than testing respiratory specimens collected by swabs, antibody tests (also called serology tests) check your blood for antibodies to SARS-CoV-2, which would indicate a past encounter with the virus. These tests involve a finger prick or a blood draw.

A highly accurate coronavirus antibody test made by Roche Diagnostics was granted emergency authorization by the U.S. Food and Drug Administration on May 3, 2020. Roche plans to dramatically ramp up its production capacity for this test.

People with antibodies in their blood may be able to donate their plasma—essentially lending another person some antibodies—for the treatment of those who are sick with COVID-19.

It’s important to understand, however, that it’s not yet certain that having antibodies to SARS-CoV-2 means you’re immune. It’s still unclear how much protection these antibodies will provide and for how long.

Medically reviewed in May 2020.

Sources:
Mayo Clinic. “COVID-19 saliva tests: What is the benefit?”
U.S. Food and Drug Administration. “FAQs on Testing for SARS-CoV-2.”
Susan Payne. “Viruses From Understanding to Investigation.” Chapter 6 - Immunity and Resistance to Viruses. Academic Press. 2017, Pages 61-71.
U.S. Food and Drug Administration. “Coronavirus (COVID-19) Update: Serological Test Validation and Education Efforts.”
U.S. Food and Drug Administration. “Policy for Coronavirus Disease-2019 Tests During the Public Health Emergency (Revised).”
U.S. Food and Drug Administration. “Insight into FDA’s Revised Policy on Antibody Tests: Prioritizing Access and Accuracy.”
World Health Organization. “Advice on the use of point-of-care immunodiagnostic tests for COVID-19.”
Roche. “Roche’s COVID-19 antibody test receives FDA Emergency Use Authorization and is available in markets accepting the CE mark.”
U.S. Food and Drug Administration. “LabCorp COVID-19 RT-PCR test EUA Summary.”
UC Davis Health. “Coronavirus (COVID-19) testing: What you should know.”
U.S. Food and Drug Administration. “Coronavirus (COVID-19) Update: FDA Authorizes First Antigen Test to Help in the Rapid Detection of the Virus that Causes COVID-19 in Patients.”
U.S. Food and Drug Administration. “Coronavirus Testing Basics.”

 

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