COVID-19 diagnostic testing is done to find out if you're currently infected with SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19).

The U.S. Food and Drug Administration (FDA) approved these types of tests for diagnosing a COVID-19 infection:

• PCR test. Also called a molecular test, this COVID-19 test detects genetic material of the virus using a lab technique called polymerase chain reaction (PCR). A fluid sample is collected by inserting a long nasal swab (nasopharyngeal swab) into your nostril and taking fluid from the back of your nose or by using a shorter nasal swab (mid-turbinate swab) to get a sample.

  In some cases, a long swab is inserted into the back of your throat (oropharyngeal swab), or you may spit into a tube to produce a saliva sample. Results may be available in minutes if analyzed onsite or a few days — or longer in locations with test processing delays — if sent to an outside lab. PCR tests are very accurate when properly performed by a health care professional, but the rapid test can miss some cases.

• Antigen test. This COVID-19 test detects certain proteins in the virus. Using a long nasal swab to get a fluid sample, some antigen tests can produce results in minutes. Others may be sent to a lab for analysis.

  A positive antigen test result is considered accurate when instructions are carefully followed, but there's an increased chance of false-negative results — meaning it's possible to be infected with the virus but have a negative result. Depending on the situation, the doctor may recommend a PCR test to confirm a negative antigen test result.

A PCR test called the Flu SC2 Multiplex Assay can detect any of three viruses at the same time: the COVID-19 virus, influenza A and influenza B (flu). Only a single sample is needed to check for all three viruses, and this could be helpful during the flu season. But a negative result does not rule out the possibility of any of these infections. So the diagnostic process may include more steps, depending on symptoms, possible exposures and your doctor's clinical judgment.

In the U.S., a COVID-19 diagnostic test is needed if:

• You have COVID-19 symptoms, such as fever, cough, tiredness or shortness of breath
• You don't have symptoms but you've had close contact with someone who tests positive for the COVID-19 virus or is suspected of having the virus. Close contact means you’ve been within 6 feet (2 meters) of a person who has COVID-19. But if you've tested positive for COVID-19 within the past three months, you don’t need to get tested. If you’ve been fully vaccinated and you’ve had close contact with someone who has the COVID-19 virus, get tested 3 to 5 days after you’ve had contact with them.
• You've participated in activities that increase your risk of COVID-19 and did not stay at least 6 feet away from others — examples include travel, large gatherings or crowded indoor settings.
• Your doctor or other health care professional or your public health department recommends a test

Certain groups are considered high priority for diagnostic testing. These include people with COVID-19 signs and symptoms who:

• Work in a health care facility or as first responders
• Live or work in long-term care facilities, such as nursing homes, or other places where people are housed closely together, such as prisons or shelters
• Are being cared for in a hospital

Other people may be given priority for testing depending on local health department guidelines for monitoring COVID-19 in individual communities.

Some people who are infected with the COVID-19 virus may be asymptomatic, meaning they don't have any signs or symptoms. But they can still transmit the virus to others. In some areas of the U.S., testing is available to asymptomatic people. If people without symptoms have a positive test result, they should follow guidelines for self-isolation to help curb the spread of the virus.

The availability of COVID-19 diagnostic testing and where to get tested may vary depending on where you live and the recommendations of your local public health officials.

There's a chance that your COVID-19 diagnostic test could return a false-negative result. This means that the test didn't detect the virus, even though you actually are infected with it. You risk unknowingly spreading the virus to others if you don't take proper precautions, such as following social distancing guidelines and wearing a face mask when appropriate. There's also a chance that a COVID-19 rapid antigen test can produce false-positive results — indicating an infection when actually there isn't one — if instructions aren't carefully followed.

The risk of false-negative or false-positive test results depends on the type and sensitivity of the COVID-19 diagnostic test, thoroughness of the sample collection, and accuracy of the lab analysis.

Be wary of any offers for at-home COVID-19 tests that the FDA has not cleared for use — they often give inaccurate results.

Whether or not you have symptoms, plan to wear a face mask to and from your doctor's office or the testing center, and have anyone who comes with you wear one, too.

• If you think you may have COVID-19, call your doctor's office or your local health department to review your symptoms and ask about testing before you go in, so staff can prepare for your visit, wearing personal protective equipment.
• If you have no symptoms but you've been in close contact with someone who has COVID-19, follow the testing advice of your doctor or public health department. Having a COVID-19 test 5 to 7 days after you were close to the person with COVID-19 is best. If you're tested too soon, the test may not detect the virus.

If you think you may have COVID-19, call your doctor's office to review your symptoms, if any, and ask about testing. Then your doctor and other staff can prepare for your visit, wear personal protective equipment, and give you instructions about where to go and how the test will be done. Plan to wear a face mask to and from the testing center, and have anyone who accompanies you wear one, too.

If you have no symptoms and have not knowingly been in contact with someone infected with the COVID-19 virus, but you want to get tested, ask your health care provider whether and where testing is available. Or you can call your state or local health department or visit their website for information on testing.

For a COVID-19 diagnostic test, a health care professional takes a sample of mucus from your nose or throat, or a sample of saliva. The sample needed for diagnostic testing may be collected at your doctor's office, a health care facility or a drive-up testing center.

• Nose or throat swab. A long nasal swab (nasopharyngeal swab) is recommended, though a shorter nasal swab or throat swab is acceptable. Your doctor or other health care professional inserts a thin, flexible stick with cotton at the tip into your nose or brushes the swab along the back of your throat to collect a sample of mucus. This may be somewhat uncomfortable.

  For the nasal sample, swabbing may occur in both nostrils to collect enough mucus for the test. The swab remains in place briefly before being gently rotated as it's pulled out. The sample gets sealed in a tube and sent to a lab for analysis.

• Saliva sample. Some locations offer saliva tests. While a saliva sample may be a bit less sensitive than a mucus sample that's taken using a long nasal swab, a saliva test is easier to do and often less uncomfortable. You spit into a tube several times to provide a sample of your saliva to test. The tube is sealed before being sent to a lab for analysis.

If you have a productive cough, your doctor may collect a sputum sample, which contains secretions from the lungs, a part of the lower respiratory system. The virus is more concentrated in the nose and throat early in the course of the infection. But after more than five days of symptoms, the virus tends to be more concentrated in the lower respiratory system.

In addition to the COVID-19 diagnostic test, your doctor may also test for other respiratory conditions, such as influenza, that have similar symptoms and could explain your illness.

The FDA granted emergency use authorization for certain at-home COVID-19 test kits, including one that tests for both COVID-19 and the flu. Most of these tests require a doctor's prescription. You collect your own sample of nasal fluid or saliva at home and then send it to a lab to be rapidly analyzed. One COVID-19 test provides fast results at home without sending the sample to a lab. And the FDA recently authorized an antigen test to buy over the counter with no prescription needed, though antigen tests are not considered as reliable as PCR tests.

The accuracy of each of these tests varies, so a negative test does not completely rule out having the COVID-19 virus. Only get an at-home test that's authorized by the FDA or approved by your doctor or local health department.

Some facilities have rapid tests for COVID-19 diagnostic testing. In that case, you may get your results in less than an hour or on the same day that you're tested. Other facilities may have to send the test sample to an outside lab for analysis. If they need to send out the sample, your results may not be available until a few days later.

Your COVID-19 diagnostic test result could be positive or negative.

• Positive result. This means you currently have an active infection with the virus that causes COVID-19. Take appropriate steps to care for yourself and avoid spreading the virus to others. You'll need to self-isolate until: Your symptoms are improving, and it's been 24 hours since you've had a fever, and at least 10 days have passed since your symptoms first appeared.

  If you have severe symptoms of COVID-19 or a health condition that lowers your ability to fight disease, your doctor may recommend that you stay in isolation longer. If you have a positive result but never developed symptoms, isolate for 10 days after the test.

• Negative result. This means that you likely weren't infected with the COVID-19 virus. But a false-negative test result could happen depending on the timing and quality of the test sample.

  Even if you test negative, you could become infected in the future, so it's important to follow guidelines for social distancing, face mask use and hand-washing to avoid potential spread. Your doctor may recommend repeat testing if you continue to have symptoms.

Contact tracing

If you test positive for the COVID-19 virus — or your doctor suspects that you have the virus but you don't have test results yet — you may be asked to participate in contact tracing. Contact tracing plays a key role in limiting the spread of infectious diseases. The sooner contact tracing starts, the more effective it is in limiting virus spread.

To begin, you provide a list of people you had close contact with during the time you may have been contagious. Public health workers then get in touch with those close contacts to let them know about the exposure and their potential for being infected. Your identity is protected during this exchange of information.

The contact tracing team provides information on what close contacts can do to minimize the risk of spreading the virus. Steps may include getting a COVID-19 test, staying at home and away from others — called quarantine — after the exposure, learning about signs and symptoms, and taking other precautions.

Quarantine recommendations

If you've had close contact with someone who has COVID-19 and have been within 6 feet (2 meters) of the person, it's best to stay at home and away from others (quarantine) for 14 days after the exposure to see if you develop COVID-19 symptoms. If you have had COVID-19 or been fully vaccinated in the past three months, you generally don't need to quarantine if you have had a close contact with COVID-19.

Other options may include ending quarantine after 10 days if you don't have symptoms and don't get tested or ending quarantine after 7 days if you receive a negative test result and have no symptoms. But continue to watch for symptoms for the full 14 days.

Contact your doctor or local health department for advice on testing and quarantine recommendations.