3 Types of COVID-19 Tests

Confused about COVID-19 testing? This guide lays it all out.

Since COVID-19 began its rampant spread in 2020, we have learned that testing is vital to track and contain the spread of the disease. Many options are available for testing, including at-home tests and those conducted at doctors' offices and health care facilities. Some tests are based on mucus samples, while others use saliva or blood. Given the various options, how do you know which test is right for you? And do they all work the same way? Or tell you the same information?

We will start with the basics. As of April 2022, there are two categories of COVID-19 tests: diagnostic tests that look for active COVID-19 infection in your mucus or saliva, and blood tests that show past infection through the presence of antibodies—evidence that your immune system has encountered the infection before.

Let's say your doctor orders a diagnostic test to confirm or rule out you are infected with SARS-CoV-2, the virus that causes COVID-19. Even among those tests, important differences exist. According to Daniel D. Rhoads, MD, section head of microbiology at the Cleveland Clinic, there are a couple of ways to detect the virus. Some tests look for a piece of the coating of the virus—they're called antigen tests—and other tests detect nucleic acid (such as RNA) belonging to the coronavirus. According to the Centers for Disease Control and Prevention (CDC), tests that identify RNA sequences are known as nucleic acid amplification tests, or NAATs.

Diagnostic viral tests can either be rapid tests or laboratory tests. Rapid tests produce results in minutes and can include antigen tests but also some NAATs.

Laboratory tests are RNA tests that use a variety of methods to detect the virus. One method involves a polymerase chain reaction (PCR) test, a lab technique used to detect the virus's genetic material, explains the U.S. Food and Drug Administration (FDA). Laboratory tests are highly sensitive but can take days to get a result.

"RNA tests also can remain positive for up to 3 months, even after somebody is no longer experiencing symptoms. Luckily, these patients are not likely infectious," Dr. Rhoads told Health.

Antigen tests are rapid tests that are generally quick and cheap but often less accurate than RNA tests. That means antigen testing is more prone to false negative results and more likely to miss cases of active infection.

"And neither antigen nor RNA testing predicts when someone is no longer contagious," said Dr. Rhoads. Since the virus can be detected after recovering from COVID-19, the CDC recommends relying on symptoms rather than test results to determine when someone can safely end any quarantine measures.

Getting the Right COVID-19 Test

The right test depends on the goal, such as confirming an active COVID-19 infection; identifying asymptomatic or pre-symptomatic individuals to follow CDC isolation guidelines, or determining whether someone previously had COVID-19. "There is not a lone testing approach that is going to meet every need and solve every problem," said Dr. Rhoads.

Here's what you should know about the different COVID-19 tests, how they're used, and what they can tell you.

Diagnostic Tests

Laboratory Tests

In most cases, a health care provider will collect mucus from your nose or throat using a specialized swab. (Some molecular tests now use saliva, which people may find more comfortable.) Turnaround time varies from minutes to days or longer, depending on whether the sample is analyzed onsite or sent to an outside lab, explains the Mayo Clinic.

But at-home test kits have become available, allowing people to collect their own sample (mucus or spit) and get results within a few minutes. These test kits are easy to use and perhaps less intimidating than long-swab testing used in health care settings. Plus, one small study from 2020 suggests that when people are taught the proper technique for collecting their own sample, self-testing yields results that can be just as accurate as those performed by health care workers.

Antigen Tests

Antigen tests are rapid tests that consistently have a quicker turnaround time than RNA tests. Also, antigen tests are cheaper to produce, making them ideal for screening large numbers of people, like at airports, a 2020 article in the journal Nature points out.

From a patient's point of view, antigen testing works in much the same way as molecular testing. Your health care provider will swab the back of your nose or throat to collect a sample for testing. If you test positive, it's probably correct: Antigen tests are highly accurate. The problem is, these tests are more likely to miss active infection. If you have COVID-19 symptoms but test negative, your doctor may order a molecular test just to rule out a false negative.

Like some NAATs, antigen tests can be performed right at your health care provider's office, meaning you don't have to go to a lab for testing. Sindhu Aderson, MD, of Chicago-based Northwestern Immediate Care, said, "these point-of-care tests are mostly used in emergency departments, doctor's offices, and outpatient clinics."

Antibody Test (Serology Test or Blood Test)

This test looks for antibodies to the coronavirus. Antibodies are proteins your immune system produces to fight off a foreign invader, such as a virus. A COVID-19 antibody test cannot diagnose active coronavirus infection, especially since antibodies do not become detectable until at least several days after an infection has started. Antibodies also can be detected if someone has been vaccinated for COVID-19. So, while the test may indicate a past infection, it can also show an immune response from being vaccinated.

There are no FDA-authorized, at-home antibody tests. You'll have to see a health care professional, who will take a blood sample via a finger prick or a blood draw from a vein in your arm. The vast majority of these tests are performed at a central lab, which can take a couple of days to process. But in September 2020, the FDA approved the first antibody point-of-care test, making it possible for doctor's offices, hospitals, urgent care centers, and emergency rooms to get an answer within 15 minutes using blood from a person's fingertip.

Antibody testing isn't recommended until at least 14 days after the start of symptoms, says the Mayo Clinic. If you test too early—while your immune system is still mounting its defense—it may not provide an accurate result. Sometimes antibody testing is done along with viral testing when someone seeks care late in the course of their illness. It may also help confirm a diagnosis of multisystem inflammatory syndrome in children, a condition linked to COVID-19.

If you have antibodies to the virus that causes COVID-19, does that mean you have immunity against future COVID-19 infections? According to the Mayo Clinic, people who have had COVID-19 and have tested positive for antibodies should not assume they are immune from getting COVID-19 again. And the CDC also emphasizes that antibody testing cannot determine immunity from COVID-19 after vaccination.

Antibody testing has a role to play in the pandemic because it can provide information on the prevalence of the infection in the population and the frequency of asymptomatic infection, per the FDA.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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