There are two main types of 2019 coronavirus disease (COVID-19) tests available.
– Diagnostic (viral) tests: use a respiratory sample (nasal swab or saliva sample) to determine if someone currently has COVID-19.
– Antibody test (also called a serologic test): A blood test to identify if someone has had COVID-19 at some point in the past.
Diagnostic tests to detect current infection
How is a diagnostic test performed?
The first step in a diagnostic test is to obtain a sample by inserting a swab (similar to a long cotton swab) into the nose or throat, or by collecting saliva. This sample is then sent to a laboratory for testing to detect the presence of the virus that causes COVID-19. If you have COVID-19 symptoms, you should be isolated at home while waiting for test results.
Who should receive the COVID-19 diagnostic test?
People who have not received the full-validity COVID-19 vaccine should continue to be tested for COVID-19 regardless of whether they are symptomatic or not. In particular, you should be tested if you are
– are symptomatic
– Have been in close contact with someone who has a confirmed COVID-19 diagnosis or who has COVID-19 symptoms
– Have recently attended a large indoor party
– Have traveled recently
– Plan to go to a large event or visit someone who is at higher risk of developing severe COVID-19
Full-activity vaccination means two weeks after the completion of the second dose of the double-dose vaccine and one week after the completion of the single-dose Johnson & Johnson vaccine. If you have not been vaccinated and have frequent contact with people at work or socially – especially if you are in close contact with others indoors without a mask – you should consider getting tested regularly.
People who are fully vaccinated against COVID-19 and those who have had and recovered from COVID-19 in the past three months do not need to be tested unless they develop COVID-19 symptoms. Certain settings or situations may have different testing requirements, such as in schools and group living facilities.
What are the different types of COVID-19 diagnostic tests?
There are two types of COVID-19 diagnostic tests available.
– Molecular tests (often called PCR or nucleic acid amplification tests) – These tests are used to detect the genetic material of COVID-19 pathogenic viruses. Molecular tests usually require a sample to be sent to a laboratory, which is why it usually takes several days for results to be available.COVID-19 molecular tests are very accurate because they can detect even if you have only a small amount of virus in your body.
– Antigen testing (often called real-time testing [POC] or rapid testing) – This test measures the specific proteins in the COVID-19 pathogenic virus. Antigen tests are relatively inexpensive and can be processed in the health care provider’s office rather than in the laboratory. As a result, results can often be obtained quickly (less than an hour). However, COVID-19 antigen testing is not as accurate as molecular testing. There are both false positive test results (the person tested is not infected with COVID-19 but tests positive) and false negative test results (the person tested is infected with COVID-19 but tests negative), with false negative test results being more common. Given this, in some cases it is recommended that healthcare providers follow up with molecular testing to confirm the test results, such as when someone has symptoms of COVID-19 but has a negative antigen test result.
What is an at-home test?
COVID-19 home testing means that some or all of the testing process can be done at home. The home test kit provides the necessary supplies to collect the sample yourself (such as a swab and a contamination-resistant container or bag to hold the swab). Some home tests must be sent to a lab for testing, and the results usually take several days to come back; other home tests allow you to perform the test yourself at home without sending the sample to a lab. For tests that are available by prescription, you should inform the health care provider who prescribed the test to you of the results.
How do I know which COVID-19 diagnostic test to get?
Your health care provider can help you determine the most appropriate type of test based on the reason you are being tested (e.g., recent exposure, symptoms, or regular testing). If you were tested for antigens, depending on your test results and the reason for the test, your health care provider may also recommend that you undergo additional molecular testing to confirm whether you have COVID-19.
What does a positive diagnostic test result mean?
A positive test result means that you probably now have COVID-19 and that you must stay home and take precautions to reduce the risk of spreading the virus to others.
What does a negative diagnostic test mean?
A negative test result means that you are probably not currently infected with COVID-19. You should continue to maintain good hand hygiene and body distance and wear a face mask. It is especially important to continue to take precautions if you are symptomatic, as you may have the virus and not be able to detect it. If you are symptomatic and are in quarantine pending test results, you cannot end your quarantine based on a negative antigen test result; to confirm your test results and end your quarantine, you must undergo molecular testing. This is because antigen testing can yield false negative results. When making decisions based on test results, it is always important to consider the type of test you are receiving. For example, if you live with or plan to visit someone who is at high risk for developing COVID-19 severe disease, keep in mind that molecular testing is more accurate.
Will I test positive for COVID-19 if I have received the COVID-19 vaccine?
The vaccine will not cause you to develop COVID-19 or cause you to test positive for COVID-19. These vaccines do not contain the virus that causes COVID-19. If you test positive for COVID-19, it means you may have been recently exposed to the virus and have COVID-19.
What are antibodies?
Antibodies are special proteins that the body produces to help fight infection. Antibodies may be produced even if a person has few or no symptoms. Sometimes antibodies protect us from getting the same infection again, and this may be true for COVID-19.
What is the purpose of COVID-19 antibody testing?
Antibody testing can help us better understand COVID-19, including how the body reacts to the virus and how likely the virus is to cause a symptomatic infection. It can also help us estimate how many people may have had COVID-19. We do not recommend relying on the results of the antibody test to decide whether to get vaccinated. People should be vaccinated regardless of antibody test results and whether they have had COVID-19 before.
Who can be tested for antibodies?
It takes time for people to develop antibodies when they are sick, so antibody testing will not be accurate for people who are sick or have recently been sick.
The test will not be accurate. Antibody testing should not be performed on people who have current COVID-19 symptoms, have had COVID-19 symptoms in the past two weeks, or have had antibodies in the past two weeks (by date of sampling).
Antibody testing should not be performed on individuals who have current COVID-19 symptoms, have had COVID-19 symptoms within the past two weeks, or have had a positive COVID-19 diagnostic test result within the past two weeks (based on the date of sampling).
How is the antibody test performed?
Antibody testing involves obtaining a blood sample by fingertip puncture or by drawing blood from a vein in the arm.
What does a positive antibody test result mean?
A positive test result means that antibodies have been detected in your blood and that you may have had COVID-19 at some point in the past; however, it is also possible that you did not have COVID-19 and that the antibodies detected are from an infection with the virus in question. This is sometimes called a false positive.
What does a negative antibody test mean?
A negative test result means that no antibodies were detected in your blood and you probably do not have COVID-19. However, it could also mean that you have had COVID-19 but: have not had enough time to produce antibodies; or your body has not produced enough antibodies to detect it; or there is a problem with the accuracy of the antibody test used.
If I test positive, does that mean I am immune to COVID-19?
No. Antibody testing can play an important role in determining whether a person may have been exposed to the COVID-19 virus and may have developed an immune response. However, antibody testing should not be used to determine if a person is immune or protected against COVID-19. Although previous infections can provide some protection, you may still develop COVID-19 again.
If I have been vaccinated against COVID-19, will I test positive for antibodies?
No. It is not recommended to get an antibody test after vaccination. Antibody testing should not be used to determine if a person is immune or protected against COVID-19, especially if a person has already received COVID-19 vaccine. Currently licensed antibody tests have not been evaluated to determine what level of immunity or protection can be achieved from COVID-19 vaccination. In addition, some antibody tests do not detect the type of antibody produced as a result of vaccination, so a negative antibody test result does not mean that the vaccine is not working. In addition, our bodies receive other defenses from vaccines, including T cells (special white blood cells that fight off infections), which are not detected by antibody tests.
If I test positive for antibodies, am I safe to be with my family and others?
A positive test result means that you may have had COVID-19 at some point in the past, and given the time that has passed, you may not be infectious because of that infection. However, it is possible to become re-infected with COVID-19.
Will my test result affect my ability to go to work?
No. Neither you nor your employer should make any decision about going to work based on a positive or negative antibody test result. Regardless of the test result, you should continue to wear your mask and use the personal protective equipment recommended by your employer.