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What to Know About COVID Antibody Tests

Updated: May 1, 2020

In the minds of most American physicians, what’s new and exciting this week is the rapidly evolving state of COVID antibody tests and their impact on the next phase of the pandemic. As we all know, we’ve been in various stages of shutdown/NPI since early March in order to “dampen the curve”, to prevent the rapid spread and crushing impact of a large number of severe cases of COVID on our health care system, especially our hospitals and ICUs.  Americans have still perished (55,000 deaths as of this week) and we’ve had millions of less severe and mild cases of illness. Please remember that the goal of the shutdown, of dampening the curve, was to avoid having AT LEAST 100-300,000 deaths, to run out of hospital and ICU beds and ventilators, and to avoid a complete medical and economic catastrophe. Our economy has suffered tremendously and our people have paid an awful price.  Yet from the viewpoint of medical providers, March and April were terrible but could have been so, so, so much worse.  

Now that the curve is flattening and we are seeing a slower rate of rise in daily deaths, the next phase of the pandemic is to open up our economy, our homes and schools, and get back to “regular” life as safely as possible while minimizing unnecessary death and suffering. Contrary to what some will tell you, this is not simple. Unlike countries that had widespread early testing, it is remarkably difficult to make good projections about the next phase without knowing the number of people who are actually infected or who have been infected.  We can make projections based on infectivity, transmissibility, and the experience of other populations and pandemics, but the key to understanding immunity to COVID and the next phase of the pandemic is antibody testing

The CDC refers to the US antibody testing programs as “Serologic Surveillance”. This is a great term: it reminds us that antibody tests indirectly spy on a virus’s activity in a population or in a particular person over time. An antibody test only tells us that COVID has been present, the immune system has generated an IgG antibody that is specific for COVID and shows that the immune system has seen COVID virus in the past.  Antibody testing does not tell us whether you or the community “were sick”, “are protected”, “can return to work”, or “won’t get sick with COVID”. 

Antibody tests are markedly different than the current NP swab test that is offered in community group testing or at your doctor’s office.  The NP swab test is an RT-PCR test that looks for active infection with the actual viral particles.  Interestingly, we might be able to do this same very accurate PCR test on saliva soon, which will change the marketing of RT-PCR vs antibody tests dramatically.  But for now, we are able to test whether you have the infection (RT-PCR) and now we begin to test whether you have had the infection in the past(antibody test). Ideally, we’d like the antibody tests to be as reliable and accurate as the RT-PCR test. And that’s where the fun part of the discussion begins.

First there were no tests, then one, now many. The first COVID antibody test for doctors’ offices made by Cellex, a company in North Carolina, and was approved by the FDA early in April. Three others were released this week.  You can expect in May and June to see at-home testing, saliva testing, in-office testing, a variety of tests with varying accuracy and reliability. Yet keep in mind: the FDA is allowing these tests to go to market through Emergency Use authorizations, i.e. without the normal rigorous level of FDA pre-market evaluation. In the UK, a widely used COVID antibody test was found- after release- to be not reliable and not useful.  So please keep in mind that many drugstore and other new COVID antibody tests may empty your wallet and not provide you with useful or helpful information. Remember: antibody tests are a snapshot in time that only show whether you have been exposed to COVID in the past. They are a part of our serologic surveillance of the US community. They don’t say whether you are “protected against COVID”. 

As of late April, I think Americans should have antibody testing in two situations: 1) when their community is doing expanded testing and asks for participation and 2) when their doctor advises a test. The COVID antibody testing situation is changing rapidly though and our access to affordable and valid tests may change soon.  But for now please remember that the new antibody tests on the public market provide (somewhat useful) data on a moment in time and only tell you whether your immune system has seen COVID in the past. To repeat, be careful and don’t generalize or misunderstand what these tests are for.  

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