COVID-19 diagnostic testing
You may have COVID-19 diagnostic testing done to find out if you're currently infected with the virus that causes coronavirus disease 2019 (COVID-19).
The U.S. Food and Drug Administration (FDA) approved these types of tests for diagnosing COVID-19:
RT-PCR test. Also called a molecular test, this COVID-19 test detects genetic material of the virus using a lab technique called reverse transcription polymerase chain reaction (RT-PCR). A health care professional collects a fluid sample by inserting a long nasal swab (nasopharyngeal swab) into your nostril and taking fluid from the back of your nose. A sample may be collected by using a shorter nasal swab (mid-turbinate swab) or a very short swab (anterior nares swab). In some cases, health care professional inserts a long swab 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 in 1 to 3 days — or longer in locations with test processing delays — if sent to an outside lab. RT-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 health care provider may recommend a RT-PCR test to confirm a negative antigen test result.
A RT-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. 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 testing process may include more steps, depending on symptoms, possible exposures and your provider's clinical judgment.
Why it's done
In the U.S., a COVID-19 diagnostic test may be needed if:
- You have COVID-19 symptoms, such as fever, cough, tiredness or shortness of breath.
- You've had close contact with someone with COVID-19. Even if you don't have symptoms, the Centers for Disease Control and Prevention (CDC) recommends getting tested at least five days after the exposure.
- Your health care provider, other health care professional or your public health department recommends a test and you're not fully vaccinated.
- You're required to take a test for screening purposes, such as at some schools or workplaces.
- Your community risk level is medium or high for the spread of COVID-19 and you plan to be around someone who has a high risk of severe illness from COVID-19.
But even in cases when a test might be suggested, you may not need to test if you've had COVID-19 in the last 30 days and you don't have symptoms.
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 have COVID-19 may not have symptoms (asymptomatic). But they can still spread the virus that causes COVID-19 to others. People with no symptoms can be tested. 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. If you have symptoms, you risk unknowingly spreading the virus to others if you don't take proper precautions, such as wearing a face mask when appropriate. There's also a chance that a COVID-19 rapid antigen test can produce false-positive results if you don't follow the instructions carefully. False-positive results mean the test results show an infection when actually there isn't one.
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.
How you prepare
Whether or not you have symptoms, plan to wear a face mask to and from your provider's office or the testing center.
- If you think you may have COVID-19, call health care provider's office or your local health department to review your symptoms and ask about testing before you go in. This way staff can prepare for your visit and wear 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 health care provider or public health department. Having a COVID-19 test at least 5 days after you had close contact to the person with COVID-19 is best. If you're tested too soon, the test may not detect the virus.
If you have no symptoms and don't think you've been in contact with someone with COVID-19, but you want to get tested, ask your health care provider or testing center whether and where testing is available. Or you can call your state or local health department or visit their website for information on testing.
What you can expect
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 or very short nasal swab or throat swab is acceptable. A 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 health care provider 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 health care provider may also test for other respiratory conditions, such as the flu, 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. Some of these tests require a provider'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. Some COVID-19 tests provide fast results at home without sending the sample to a lab.
You can buy some antigen tests over the counter with no prescription needed, though antigen tests are not considered as reliable as PCR tests. The benefits of an at-home test are you can take it at home and get quick results. It's a fast and easy way to test yourself as soon as you have symptoms or at least five days after you've been exposed to the COVID-19 virus. It's also an option if you want to make sure you don't have the virus before meeting in groups with others, to ensure you don't accidentally spread it. If you test negative, taking the test a second time a few days later can help ensure your test results are accurate.
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. Avoid spreading the virus to others.
You'll need to isolate for at least five days. After that it's OK to be around others who are at average risk for severe disease if your symptoms are improving, and it's been 24 hours since you've had a fever without use of fever-reducing medication. Wear a mask for five more days. If you have COVID-19 home tests, you can take tests two days apart, starting on day six. If your results are negative on both tests, you can stop masking. If you don't do the home test, wear a mask around others for 10 days.
If you have severe symptoms of COVID-19 or a health condition that lowers your ability to fight disease, your health care provider may recommend that you stay in isolation longer. If you have a positive result but never developed symptoms, isolate for five days after the test and wear a mask for five more days.
Negative result. This means that you likely don't have an infection with the COVID-19 virus. But a false-negative test result could happen depending on the timing and quality of the test sample. If you have symptoms, stay away from others. Your doctor may recommend repeat testing if you continue to have symptoms.
Even if you test negative, you could become infected in the future. So it's important to follow guidelines for vaccination, physical distancing, ventilation, face mask use and regular hand-washing to avoid potential spread.
If you test positive for the COVID-19 virus, you may be asked to participate in contact tracing. Contact tracing plays a key role in limiting the spread of infectious diseases, as it can help limit virus spread. Public health staff may ask you for a list of anyone you had close contact with during the time you may have been contagious. Public health staff may contact these people. They may suggest that your contacts watch for symptoms, get COVID-19 tests or stay at home and away from others if they're not vaccinated.
© 1998-2023 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved.