For a brief moment this summer ― when coronavirus cases and hospitalizations plummeted around the U.S. ― COVID-19 testing seemed much less important than it did earlier in the pandemic. Then the delta variant thrust the country into another devastating wave of cases.
Fortunately, tests are widely available at this point ― and the turnaround time tends to be much faster, too.
“It really is pretty easy to get a test these days, unless you’re living in a more remote area,” said Stan Spinner, vice president and chief medical officer of Texas Children’s Pediatrics and Texas Children’s Urgent Care.
But with so many testing options, knowing what to get — and when — can be confusing. Here’s a breakdown of the leading COVID-19 testing options:
Laboratory molecular or PCR tests
How they work: Molecular COVID-19 tests are one of the two diagnostic tests than can tell if you have an active COVID-19 infection. They detect the genetic material, or RNA, of the coronavirus. These tests generally require a swab sample to be taken from your nose — though how far up your nose the swab goes can vary. Some swabs go just inside the nostril, while others extend much farther into the nasal cavity.
Although the terms “molecular” and “PCR” tests are often used interchangeably, not all molecular tests use a polymerase chain reaction (PCR) to detect the presence of a virus. But PCR tests really are the mainstay of COVID-19 testing.
How accurate they are: PCR tests are the “gold standard,” as Spinner put it. They’re highly sensitive (meaning they correctly identify those with the virus) and specific (meaning people don’t often get false results).
There isn’t a consistent percentage of how accurate these tests are, because that depends on a number of factors like how soon the test is conducted after an exposure or what type of swab someone uses. A Cochrane review of rapid, point-of-care tests found, for example, that PCR tests correctly diagnose 95% of COVID-19 cases — and correctly rule out infection 99% of the time — but noted there remain significant questions about how well those results hold up in real-world settings.
Still, experts are in agreement that if you want the most accurate results, PCR tests are the way to go.
“The majority of us in the health care industry really feel the most comfortable doing the PCR test, which is that gold standard,” Spinner said.
When you should take one: Because lab-done PCR tests are considered the most accurate COVID-19 tests, they should be your go-to if you’ve developed symptoms or believe you’ve been in close contact with someone who is positive for COVID-19.
The turnaround time is often around two or three days, but that depends greatly on the facility where you’re getting it done and what its capacity is.
Some point-of-care centers can turn around PCR tests on the same day — or even under an hour — depending on their testing capacity and location. They’ll often market “rapid PCR tests,” which refer to real-time reverse transcription-polymerase chain reaction testing, or RT-PCR. These are a slight variation on PCR testing and can deliver results quickly. But, in general, if you’re a consumer walking into a facility to get a rapid test right now, you’re likely getting an antigen test (more on that below).
Rapid antigen tests
How they work: When people talk about “rapid” tests, they’re generally referring to antigen tests, which work by looking for bits of protein from the SARS-CoV-2 virus.
Just like PCR tests, samples are generally collected via nasal swabs, though throat swabs are also possible. The swabs are then treated with a chemical reagent and analyzed on site by a health care professional, giving you results within minutes.
How accurate they are: Antigen tests are much less reliable than PCR tests. The recent Cochrane review found they correctly identified COVID-19 in 72% of people with symptoms, but in just 58% of people without symptoms.
Antigen tests require a higher level of the virus in the test sample for the sample to turn positive, so false negatives are a particular concern — especially among people who might be asymptomatic.
When you should take one: Because they’re less accurate, and because they may lead to missed asymptomatic cases, health experts are torn on the usefulness of rapid tests. Their obvious advantage is speed. Some countries are deploying them in airports, for example, to quickly screen people who are traveling from high-transmission areas. Rapid tests might also be more useful if they’re administered daily or every few days in environments like movie sets and with sports teams, Spinner said. That is a strategy called serial testing.
But in general, the rapid antigen test “is not great as a one-time, ‘OK, let’s see if you’re OK to go to school or go to work’ kind of test,” Spinner said.
At-home testing kits and collection kits
How they work: The Food and Drug Administration has provided emergency-use authorization for several at-home collection and at-home testing kits, which are two different things.
The agency has not approved any PCR tests for at-home testing, but there are collection kits you can use to provide a sample yourself, then send that sample into a lab that will conduct the PCR test for you. The FDA has also approved full at-home testing kits, which are antigen tests you can take at home and can give results in minutes.
How accurate they are: At-home tests and at-home collection kits are generally believed to be less accurate than in-lab PCR and antigen tests, largely because how someone collects the samples really matters.
“They’re probably the least accurate of any of the ways of testing because A, there’s no one supervising the technique to obtain the swab, whether it’s in their nose or on the side of the mouth, and then B, the actual antigen tests themselves are less accurate than the PCR tests,” Spinner said.
When you should take one: At-home tests are useful if access is a problem, so if you’re in an area where it’s not easy to head to a medical center or lab. They can also be helpful in situations where people are really wary or fearful of being tested, or if someone needs to be quarantined and they want to do the test as a first step.
Some at-home tests are designed for serial testing, meaning you take several tests over the course of multiple days, so they can be one part of an effective preventive strategy. “By testing more frequently, you might detect COVID-19 more quickly and could reduce the spread of infection,” according to the Centers for Disease Control and Prevention.
How they work: Antibody or serology tests are blood tests or finger pricks that look for COVID-19 antibodies that indicate prior infection or vaccination. They are not intended to diagnose current COVID-19 infection.
How accurate they are: In one Cochrane review, antibody tests given a week after people’s COVID-19 symptoms appeared were only about 30% accurate. By the third week, that increased to about 90% accuracy. But there’s little evidence about what happens after that.
Even if a test accurately picks up antibodies, it’s not clear how useful that information is to most people. No one knows what concentration of antibodies is needed to provide really good, strong protection against the coronavirus, which is why antibody tests shouldn’t be used to “evaluate a person’s level of immunity or protection from COVID-19,” the FDA says.
When you should take one: Antibody testing is not currently recommended to assess if you’re immune to COVID-19 after getting vaccinated, the CDC says, nor is it routinely recommended to determine whether you had COVID-19 before and did not know it.
However, antibody tests can be useful from a public health perspective, and they can serve a purpose in certain clinical care settings, like if doctors are trying to determine whether a young patient has multisystem inflammatory syndrome in children, or MIS-C, or if they’re treating a patient with suspected long-haul COVID-19 (although not everyone who develops long-term symptoms will have a positive antibody test or tests).
So when should I get tested?
Experts say we are once again in a moment when it is essential to err on the side of getting tested.
Anyone with symptoms of COVID-19 — including those who are fully vaccinated — should now get tested for the virus. The CDC recently updated its guidance to reflect that the delta variant is more contagious and that people who are fully immunized might be able to transmit the virus.
Additionally, you should get tested if you have come into close contact (within 6 feet for more than 15 minutes over the course of 24 hours) with someone who has tested positive for the virus, the CDC says, regardless of your vaccination status and whether or not you’re experiencing symptoms.
“With the delta variant, we know that typically one infected person will infect six or seven others in their environment,” Spinner said.
“It is incredibly contagious, so it is so important to do the right thing. If you think you may have it or your child may have it, get tested,” he added. “And if you have it, stay home and isolate.”
Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.