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Dr. Richard Ellin Gives Update on COVID-19 Testing
There are a variety of tests and testing procedures for COVID-19. Understanding them all can be confusing. I will try to provide some basic information regarding the various types of tests that are available.
There are basically two different types of tests for COVID-19:
1) Diagnostic Tests can show if you have an active coronavirus infection and should take steps to quarantine or isolate yourself from others.
2) Antibody Tests look for antibodies that are made by your immune system in response to a threat, such as the coronavirus.
Among the diagnostic tests which detect the virus, there are currently two types: 1) molecular tests, such as RT-PCR tests, that detect the virus’s genetic material (RNA), and 2) antigen tests that detect specific proteins on the surface of the virus.
Molecular tests are typically run on swabs taken from the nasopharynx or throat, or occasionally from saliva. Results can be available within one day, although because of the overwhelming demand for tests, they are often taking several days or even more than one week to come back. These tests are highly accurate, especially if done from a nasopharyngeal swab. This is the type of test done most commonly at drive thru testing sites or other facilities.
Antigen tests are sometimes referred to as “rapid diagnostic tests.” They are also run on a nasal or throat swab, and can provide results same day, often within one hour. Positive results are highly accurate, but if a result comes back negative in someone highly suspicious for COVID-19 (ie false-negative), then it’s often appropriate to run a molecular test to confirm the result.
As opposed to these diagnostic tests, antibody tests look for the antibodies that fight COVID-19 infection. There are at least two types of antibodies that we can produce after exposure to COVID-19, and they can take several days or weeks to develop after you have an infection. They may stay in your blood for several weeks or more after recovery. Recent research indicates that in most people who have COVID-19 and have no or very mild symptoms, the antibodies become undetectable in the bloodstream about five-six weeks after infection. Antibody tests should not be used to diagnose an active coronavirus infection, nor should they be used to confirm or rule out that someone has had COVID-19. We also do not know if the presence of antibodies means that you are immune to the coronavirus in the future. Therefore, at present, antibody tests are useful for research and public health purposes and can be used to identify individuals that may be candidates for donating convalescent plasma. However, they are otherwise of no clinical use to individual patients.
Dr. Richard Ellin