What you need to know about getting tested for coronavirus

Long lines, slow results and inconsistent advice have left many of us confused about when and how to get tested. We talked to the experts to answer your questions

Testing is essential to controlling the coronavirus. Once people know they are infected, they can isolate, alert others of the risk and stop the spread.

But months into the pandemic, many people still are frustrated and confused about virus testing. Long lines at testing sites, delays in getting results and even surprise testing bills have discouraged some people from getting tested. Many people don’t understand what a test can and can’t tell you about your risk — and wrongly think a test result that comes back negative guarantees they can’t spread the virus to others.

We asked some of the nation’s leading experts on testing to help answer common questions about how to get tested, what to expect and what the different tests and results really mean. Here’s their advice:

When should I be tested for coronavirus?

Ideally, you should be able to get a coronavirus test whenever you want it. But in the United States, test availability varies around the country. In some places, you still need a doctor’s prescription to get tested. In other communities, you can get tested easily by walking in to a clinic or even using a home test kit. There are four main reasons to get a test.

Symptoms: Feeling sick is the most urgent reason to get tested. A dry cough, fatigue, headache, fever or loss of sense of smell are some of the common symptoms of Covid-19. (Use this symptom guide to learn more.) While you’re waiting for your results, stay isolated from others and alert the people you’ve spent time with over the last few days, so they can take precautions. Many tests are most reliable during the first week you have symptoms.

Exposure: Did you find out that you recently spent time with an infected person? Were you in a risky situation, like an indoor gathering, or a large event or in an airport and airplane? You should quarantine and get tested. If testing isn’t widely available and you have only one chance to take a test, it’s best to get tested five to six days after a potential exposure to give the virus the opportunity to build up to detectable levels in the body. Test too early, and you might get a false negative result. If you’re in a city where it’s easy to get a test, get tested a few days after the exposure and, if it’s negative, get tested again in three or four days. If you think you’ve been exposed to the virus, the Centers for Disease Control and Prevention advises you quarantine for at least seven days and receive a negative test result before returning to normal activity.

Precautions: Some people get tested as a safeguard. Hospitals may require you to be tested before certain invasive medical procedures or surgery. Visitors to nursing homes may be given a rapid test before they are allowed to enter. Many colleges and boarding schools test students frequently and suggest they be tested before leaving campus and when they return. If you must travel, it’s a good idea to be tested before you leave, and a few days after you arrive. A negative test result is never a free pass to mingle with others, but knowing your infection status will lower the chance that you are unknowingly spreading the virus. Check on the turnaround time at the testing site in your area, and try to time it so you get a result as close as possible to the event or visit. Even if your test result is negative, you still need to wear a mask, maintain distance from others and take other precautions.

Community testing: In some cases, local health officials will encourage widespread testing for everyone, offering tests at health clinics, pharmacies and drive-through testing sites. Testing lots of people helps measure the level of spread in an area and can help slow or stop the spread in areas where known infections have occurred. In New York City, for instance, a health department advertising campaign is encouraging people to be tested often, even if they feel fine. “We learned that one of the ways we can control this virus effectively is by making sure as many people as possible are tested at a given time, so we can pick up people who are infected but don’t yet know they have the infection,” said Dr. Jay K. Varma, deputy commissioner for disease control at the New York City Health Department.

What type of test should I get?

Virus tests are categorized based on what they look for: molecular tests, which look for the virus’s genetic material, and antigen tests that look for viral proteins. The various tests all use a sample collected from the nose, throat or mouth that may be sent away to a lab or processed within minutes. Testing should be free or paid for by your insurance, although some testing centers are adding extra charges. Here are the common tests and some of the pros and cons of each.

Laboratory molecular test: The most widely available test, and the one most people get, is the P.C.R., or polymerase chain reaction, test, a technique that looks for bits of the virus’s genetic material — similar to a detective looking for DNA at a crime scene.

Pros: This test is considered the gold standard of coronavirus testing because of its ability to detect even very small amounts of viral material. A positive result from a P.C.R. test almost certainly means you’re infected with the virus.

Cons: Because these tests have to go through a laboratory, the typical turnaround time is one to three days, though it can take 10 days or longer to get results, which can limit this test’s usefulness, since you may be spreading virus during the waiting period. Like all coronavirus tests, a P.C.R. test can return a false negative result during the first few days of infection because the virus hasn’t reached detectable levels. (One study showed that among people who underwent P.C.R. testing three days after symptoms began, 20 percent still showed a false negative.) Another frustration of P.C.R. testing is that it sometimes detects the virus’s leftover genetic material weeks after a person has recovered and is no longer contagious. The tests are also expensive, costing hospitals and insurers $50 to $150 per test.

Rapid antigen test: An antigen test hunts for pieces of coronavirus proteins. Some antigen tests work sort of like a pregnancy test — if virus antigens are detected in the sample, a line on a paper test strip turns dark.

Pros: Antigen tests are among the cheapest (as little as $5) and speediest tests out there, and can deliver results in about 15 to 30 minutes. Some college campuses and nursing homes are using rapid tests to check people almost daily, catching many infectious people before they spread the virus. Antigen tests work best when given a few times over a week rather than just once. “It tells you, am I a risk to my family right now? Am I spreading the virus right now?” said Dr. Michael Mina, an epidemiologist at Harvard University’s School of Public Health and a proponent of widespread rapid testing. Though, he cautioned, “if the test is negative, it doesn’t tell you if you’re infectious tomorrow or if you were infectious last week.”

Cons: An antigen test is less likely than P.C.R. to find the virus early in the course of the infection. One worry is that a negative rapid test result will be seen as a free pass for reckless behavior — like not wearing a mask or attending an indoor gathering. (The White House Rose Garden event is a good example of how rapid testing can create a false sense of security.) A negative antigen test won’t tell you for sure that you don’t have the coronavirus — it only tells you that no antigens were detected, so you’re probably not highly infectious today. (In one study, a rapid antigen test missed 20 percent of coronavirus infections found by a slower, lab-based P.C.R. test.) Antigen tests also have a higher rate of false positive results, so a positive rapid test should be confirmed.

Rapid molecular test. Some tests combine the reliability of molecular testing with the speedy results of a rapid test. Abbott’s ID Now and the Cepheid Xpert Xpress rely on a portable device that can process a molecular test right in front of you in a matter of minutes.

Pros: These tests are speedy and highly sensitive, and they can identify those exposed to coronavirus about a day sooner in the course of an infection than a rapid antigen test. A rapid molecular test isn’t quite as accurate as the laboratory version, but you’ll get the result much faster.

Cons: Depending on where you live, rapid molecular tests might not be widely available. They are also less convenient and often slower than many antigen tests. And like all coronavirus tests, a negative result isn’t a guarantee you don’t have the virus, so you’ll still need to take precautions. Like its laboratory cousin, a rapid molecular test can detect leftover genetic material from the virus even after you’ve recovered.