Local physician explains COVID-19 virus testing methods

Wed, 05/13/2020 - 12:15pm

    I thought an introduction to current testing available for the SARS-CoV-2 virus (the virus that causes COVID-19 disease) might help shed some light and eliminate some confusion (and maybe save some money).

    There are at present two distinct types of testing available. The first is a group of tests to determine if a person has evidence of the virus’ genetic material in their respiratory tract and the second is a test to see if a person’s immune system has made any antibodies to the virus.

    At present our testing for evidence of the virus in the respiratory tract is generally obtained by a nasal swab.  There are other versions of this test out there including a home based saliva test. The nasal swab type test is what the state and CDC are currently using to track cases of COVID-19.

    The problem with these tests (besides not being as available as they should be) is that they just aren’t as reliable as most people think they are. The governor and the state CDC hope to make these tests more widely available, but that will not change its current limitations. The nasal swab used to detect the genetic foot print of the COVID-19 causing virus is only about 80% accurate at best — and this depends a lot on timing. A person who is infected with the virus may not show symptoms for several days.  If a person who has COVID-19 were to have the test done on the first day of symptoms the likelihood of detecting the presence of the virus (it’s genetic material) is only about 50%. The likelihood of finding evidence of the virus goes up each day until about day 5 or 6 of symptoms when it reaches about 80%. That means that at least one in five people who actually have the infection will test negative. Not exactly reassuring.  Each day after that the rate of detection starts to drop over the next couple weeks.

    The other type of testing that has made a recent entry into to field and market place is antibody testing. This is a blood test. The purpose of this test is not so much to detect the presence of the virus but to detect the body’s reaction to it. The hope is that these tests may indicate ones immunity to the virus. But, so far, we really don’t even know which antibodies can indicate immunity. And, again, timing is important. In the first couple weeks of infection (or of symptoms) the results may be negative or indeterminate.

    There is a lot of energy and enthusiasm for antibody testing. There are amazing claims being made from lots of labs. There are even some claims being made by local healthcare providers about the near infallibility of tests being offered. But, there’s a reason why you will be paying out of pocket for such testing (no insurance company is yet paying for these) and one of the reasons is that none of these tests has FDA approval — Not one of the over 200 such tests. Several (at last count 12) on May 4th had received emergency use authorization (EUA) but that is a far cry from FDA approval.

    Few of the developers of these tests are being very transparent about exactly what antibodies are being detected. There are at least 8 different types of antibodies potentially being made in response to exposure to this virus. And, at this point, we have no good evidence to suggest which antibodies (if any) might be associated with some level of immunity. I’m not saying these tests are of no value — they are of great value for public health monitoring of this pandemic but may be of limited value to an individual. So I’m suggesting that at this point you should save your money. Every one of the tests currently available carries with it this regulatory statement: “The … FDA’s independent review of this validation is pending. Negative results do not rule out SARS-CoV-2 infection, particularly in those who have been in contact with the virus. Follow-up testing with a molecular diagnostic [such as a nasal swab test] should be considered to rule out infection in these individuals. Results from antibody testing should not be used as the sole basis to diagnose or exclude SARS-CoV-2 infection or to inform infection status. Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E...”

    So, if you had a pretty bad cold last fall or last year, you might have antibodies from another corona virus and that could erroneously suggest you have had exposure to COVID-19 and even lull you into thinking that you are immune to COVID-19. Anyone who tells you otherwise (and is willing to charge you for the privilege) is ignorant at best or fear mongering at worst.

    This is an area where what we know and understand is changing almost daily. True validation of many of these antibody tests will be forthcoming but isn’t here yet. I’m hopeful that testing will improve and become more available and that the results can help reduce uncertainty but for now, living with uncertainty will have to be part of the new normal.

    The opinions expressed in this piece are mine and reflect my understanding of the current state of testing to date (a rapidly changing area). But, more to the point they are mine and are not intended to represent those of other health care providers and I do not write this as a representative of LincolnHealth or of any healthcare organization.