Updated on May 21, 2020.
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.
