The Role of COVID-19 Tests
There are multiple types of tests for COVID-19. Tests can be used to detect active infection or to detect past infection or immunization.
Because people with COVID-19 can transmit the virus to others, identifying people with active infections is important to reduce the spread of the disease. In people with symptoms, testing can also help determine whether those symptoms are being caused by COVID-19, a different respiratory virus, or another condition. Early identification of COVID-19 in people who need treatment can help make treatment as effective as possible.
Testing for active infection can be used for diagnosis, screening, or monitoring:
- Diagnosis is testing for COVID-19 in people who have shown symptoms of the disease.
- Screening is testing in people who have not shown symptoms. For COVID-19, screening is often done for people who have been in close contact with someone who has tested positive.
- Monitoring is a method of follow-up to determine if a person who was previously diagnosed with COVID-19 continues to test positive.
Another role of testing is looking for indications of a prior infection with SARS-CoV-2 or prior immunization. This is known as serological or antibody testing. This type of testing can be used for research purposes to estimate how much of the population has been affected by SARS-CoV-2.
Serological testing may also be used when a person has health issues that could be related to a previous COVID-19 infection but was not tested or did not test positive before. Although antibodies may help immune defenses against COVID-19, a positive antibody test does not prove that a person has immunity.
Who should get testing?
The type of test and a person’s individual circumstances affect who should get COVID-19 testing.
Diagnostic testing for an active infection is warranted in people who have symptoms that are consistent with COVID-19.
Screening tests in asymptomatic people can be conducted in many different contexts. These tests are most often recommended when a person has been in close contact with someone who has COVID-19 or has been in a situation with an elevated risk of virus exposure such as a large social gathering.
Screening tests may be utilized in other circumstances such as:
- For residents and workers in shared living environments, especially if some individuals are vulnerable to severe illness with COVID-19. Examples of these potentially high-risk environments include nursing homes, correctional facilities, and homeless shelters.
- For all people admitted to the hospital, especially if there is significant community transmission of SARS-CoV-2.
- For patients prior to surgeries or other medical procedures.
- For patients who are being prescribed drugs that could suppress their immune system.
- For employees or students who are often in close contact to detect asymptomatic cases as part of health programs to reduce virus transmission.
Monitoring of patients can also employ tests for active infection. It is important to note, though, that a positive result on a repeat test does not always mean that a person is contagious, and likewise, a follow-up negative test result does not always mean that the individual is no longer contagious.
There are not clear guidelines for who should receive testing for past infection. Many serologic tests are conducted as part of epidemiological studies about the number of people with prior infections. An antibody test may also be appropriate in patients who have health concerns that could be late-developing complications of COVID-19.
With all of these test types, especially tests for active infections, available resources are an important factor in determining who should be tested. If testing capacity is limited, public health officials and health care providers may establish guidelines to prioritize the use of tests in specific patients or circumstances.
Talking with a doctor is the best way to determine if you should receive a coronavirus test, and, if so, which test is the best fit for your situation. It is especially important to talk with your doctor promptly if you have symptoms of COVID-19.
Getting test results
How you get test results and how long it takes to receive them varies based on the type of test:
- Tests that require laboratory analysis usually have results available within a few business days, although some of these tests can be performed more quickly. Results are normally provided by your doctor’s office or sent electronically and/or by mail.
- Point-of-care tests are designed for rapid analysis without sending a sample to a laboratory. For these tests, results are often available in minutes or hours. Results may be delivered by a health care provider or sent directly to you either electronically or by mail.
- Many at-home tests allow for your sample to be analyzed right after taking the test sample. You see the results yourself, and they are normally available in less than an hour.
High demand for testing may affect the time required to receive some test results. Reduced test availability and strained laboratory capacity may create delays in analyzing test samples.
Types of COVID-19 Tests
Viral tests that detect active COVID-19 infections are normally conducted using a sample that comes from your respiratory tract. A swab taken from your nose or throat is common, although some options exist for saliva testing.
There are two main types of these diagnostic or screening tests:
- Molecular COVID-19 tests: Also known as nucleic acid amplification tests (NAATs), molecular tests look for genetic traces of SARS-CoV-2. By first making many copies of the genetic material in your test sample, these tests can find even very small amounts of the virus’s genetic material. There are many types of NAATs, but the most common and well-known uses a laboratory method called reverse transcription polymerase chain reaction (RT-PCR), which is sometimes referred to as PCR.
- Antigen tests: Antigens are a type of protein that provoke an immune response, and antigen testing looks for antigens that are specific to SARS-CoV-2.
These tests can be performed in a laboratory setting and may be available for point-of-care or at-home testing as well. Some of these viral tests are designed to be rapid tests while others require more time to analyze.
Testing for past infections is also known as serologic testing or antibody testing. It analyzes a sample of your blood to see if there are antibodies to SARS-CoV-2. Antibodies are a protein that the immune system makes to help identify and defend against pathogens like viruses. It generally takes several weeks for some antibodies to develop, so these tests are usually not effective for detecting active infections.
The table below provides an overview of the tests available for COVID-19:
|PCR and Molecular Tests
|Detect current infection
|Nose swab, throat swab, or saliva sample
|Detect current infection
|Detect prior infection and prior immunization
Getting Tested for COVID-19
In many cases, testing for COVID-19 is done after a doctor prescribes a specific test. Testing may be prescribed for diagnosis if you have symptoms or for screening if you have had potential exposure to SARS-CoV-2.
Some types of tests are available without a prescription. Screening tests may be available in labs, pharmacies, drive-through or walk-up clinics, or for at-home use.
After a swab or saliva sample is collected, molecular COVID-19 testing is most often done by a laboratory, but some options exist for rapid analysis. Antigen tests can be conducted by laboratories but are often available in pharmacies or health clinics as a rapid point-of-care test.
Serological testing for antibodies to SARS-CoV-2 is normally conducted in a medical laboratory. A blood sample is often taken in a medical office, but options exist for at-home collection of a test sample that is sent to a laboratory.
There are several types of at-home COVID-19 testing options:
- Molecular and antigen tests that involve taking a sample at home and sending it to a lab for analysis.
- Molecular and antigen tests in which both sample collection and test analysis are conducted at home.
- Serological tests that involve a fingerstick to get a blood sample that is then sent to a lab for analysis.
Depending on the type of at-home testing that is conducted, repeat testing may be required by your physician to confirm the test result. Even without a confirmatory test, people with a positive result should isolate to avoid potentially spreading the virus to others.
It is also important to notify your doctor of a positive result so that it can be anonymously reported to your state health department for accurate tracking of COVID-19 cases in your community.
Molecular tests, such as a PCR test, that are analyzed in a laboratory are generally considered to be the most dependable tests for active infection. However, test accuracy can be affected by factors such as the laboratory method used and the type and quality of the test sample.
Antigen tests can detect current infections and are generally reliable although they are more likely than most molecular tests to return a negative result when a person is actually infected.
Rapid tests, such as point-of-care or at-home tests, are less accurate than laboratory tests, but they are still accurate in the majority of cases.
Serological tests are not designed to detect active infections, so it is important to distinguish them from molecular or antigen tests.
Depending on the situation, factors such as cost, convenience of testing, and the time required to receive results can influence the decision about which test to use. Because of fluctuating supply and demand, certain types of tests may not be available at a given time or location.
Talk with your doctor if you have symptoms of COVID-19, are concerned about a potential coronavirus exposure, or are interested in or have questions about getting tested for COVID-19. Your doctor can address the benefits and risks of testing in your situation and discuss the most appropriate type of test.