There have been many changes in testing since we first learned about COVID-19. We sat down with Panagis Galiatsatos, M.D., Assistant Professor in the Division of Pulmonary & Critical Care Medicine at Johns Hopkins School of Medicine, to answer some of our most pressing questions.
What are the different types of tests?
There are two main kinds of COVID-19 tests, diagnostic and antibody. Diagnostic tests help to diagnose the current infection while antibody tests show if you previously had the infection. Neither test can do both.
Diagnostic testing, which looks for a very specific part of SARS-Co-V2, can be further broken up into molecular and antigen tests. Molecular tests, also known as PCR tests, are considered the gold standard of testing because of precision. They require a nasal or oral swab that is analyzed for genetic material that comes from the virus. Though they take longer to process, sometimes up to a week or more, this test is highly accurate and rarely results in a false positive or negative reading, so there is a high degree of confidence in the results.
However, the big break-through, and more common test, has been rapid testing. These antigen tests require a nasal swab to identify protein fragments or antigens from the virus. This option may be more practical for real world use because results are available with 15 to 30 minutes, but this rapidity sacrifices sensitivity. False positives and false negatives are more likely to occur with antigen testing, which is why multiple tests may be required to achieve confidence in the results.
Point of care or rapid testing is not as accurate as other tests, but it beneficial because of how quickly you can get results. For example, for diabetes, a finger stick for glucose tells you your level versus going to a lab and drawing hemoglobin A1C. Though the second test is more accurate, it's going to take time for it to come back. The point of care with the fingers is much more rapid, but you sacrifice a bit of accuracy. However, if you keep doing it over and over, you're likely to increase that sensitivity. It is also much more convenient to do testing whenever deemed necessary in the comfort of your home.
What about home tests?
The average at-home test is going to be a diagnostic test that may be less invasive. The kits want to be as easy as possible, so they are most likely to be a saliva or nasal swab test. These tests have been developed to be simple for the general public to use in home situations.
Similar to rapid testing, the biggest concern is these tests sacrifice some sensitivity and accuracy. In the right setting they are definitely useful, so I do think it's reasonable for people to pursue at-home testing with the guidance of their healthcare provider. It is important to make sure the test is authorized by the FDA, and that you understand how to use it correctly to get the most accurate results.
In addition, it is important to take into account your current symptoms or possible exposure when reading the results. If you have symptoms or went to a party and later it was identified someone had COVID-19, but you are getting a negative result, your probability of infection is still high - so home testing may not be accurate enough. At the end of the day, I would still talk with your healthcare professional to discuss what the test results mean in your current context.
When should someone get tested?
I would suggest probably waiting four to five days after potential exposure before getting tested and during that time staying in quarantine to ensure you do not unknowingly infect others. That's, of course, unless symptoms kick in, but it may still take a few days to register a positive test. This is important because, like any other testing, results may not be positive if the test is taken too soon. For example, think of a pregnancy test. It's going to be negative for quite some time or it will never become positive because it didn’t capture the level of hormone it needed to get a positive reading. Similarly, with COVID-19 tests, there are so many factors that may cause it to be negative.
Where should you get tested?
There are a few things you should consider when choosing a testing location. First, you should find out what the expected turnaround time is for receiving results and this should depend on what kind of testing is being offered. Molecular tests take longer so labs may be backed up. It may take a week or longer before you receive results and at that point you should have just quarantined for an additional week while awaiting results.
That is why rapid testing may be the better first choice. However, you should also consider your symptoms. If you are having fever and chills or you know that you came in contact with someone with COVID-19 then it may be better to wait to have a test in a proper clinical setting. In addition, and regardless of the results, make sure you talk about any symptoms or contact with your healthcare professional.
Will it hurt?
I think we have gotten better in regard to making testing more comfortable. It's still a bit unpleasant, but it is only about four seconds of discomfort. I hesitate to say it's gotten better than when we first started because it's still kind of relative, so I would just say be prepared. There will be some mild discomfort which should last very briefly.
You can learn more about testing by visiting our Testing and Diagnosis page.
Blog last updated: January 13, 2021