Up until two weeks ago we had just a few COVID patients in total in my hospital and none in the ICU. For a few months we had quietly slipped back to our usual routine. We were caring for those sick with heart attacks, severe infections, drug overdoses, and other sundry calamities that can befall the human body and land someone in the ICU.

Then everything changed in just a few days.

We started getting critically ill and ventilated COVID patients, a few at a time, filling up our empty beds day after day. I was getting called to see more critically ill patients outside the ICU as well. Half of our ICU is now COVID patients and we have started overflowing our critically ill patients to other units. It feels just like it did in the spring and it all happened so fast.

You might imagine that, after a long day of seeing lives ravaged by this virus, one could be frustrated with the expressed opinions of many outside the hospital. It seems that anyone with a twitter or facebook account is now an expert, qualified to pass judgment on the CDC, Fauci, or even us medical providers. We on the frontlines often bemoan this fact when we have a moment to breathe between donning and doffing our PPE.

My medical training lasted for 10 years after college and I have been in practice for another 9 but I do not consider myself an expert on COVID-19 – certainly not enough to make up my own guidelines. Most of what I write is an attempt to explain the opinions of the experts in as simple terms as possible to help others understand the source of these guidelines and bring some order in the chaos. I mention this only to give you the context to understand how it feels to hear people who have only spent a few hours reading reports on social medial handing down judgment with passion and certainty about matters related to this pandemic. One must not confuse confidence with correctness. It’s even worse because the consequences of the bad information they spread is, quite literally, deadly.

This is often my experience when hearing people discuss antibody testing. It seems that many people have a dangerously rudimentary and overly simplistic understanding of all aspects of immunity and the antibody response is no exception. Their logic goes like this. Viruses are bad. They seem to remember vaguely someone teaching them in middle school biology that antibodies fight viruses and make people immune to infection. Ergo, if they have a test showing the presence of antibodies to SARS CoV-2 this means they are protected from future infection. While this logic seems valid, it relies on the following assumptions, many of which may not be true:

  1. The test results are accurate at detecting the desired antibodies. In other words, the test is from a company with reliable protocols, reagents, and facilities to accurately detect antibodies to SARS CoV-2 in a sample of blood. There have been many dubious enterprises peddling their testing directly to consumers which do not give accurate results. There are nearly 100 commercially available serologic assays. They are highly variable, differing in their format, the antibody class detected, the targeted antigen, and the acceptable specimen types. There is no standardization or quality assurance.
  2. The antibodies the test detects are to SARS CoV-2. There are may coronaviruses in the world and there can be cross reactivity in the tests. This would create a situation where someone who had antibodies to another coronavirus would get a test result incorrectly showing antibodies to this coronavirus.
  3. The level of antibodies reported is enough to confer protective immunity. It is possible that a minimum quantity of antibodies is necessary to protect from future infection. It may be that mild infections lead to lower antibody levels. It may also be that severe infections have lower antibody levels because of faulty antibody production – a mechanism that could lead to more severe disease.
  4. The protection persists. Other coronaviruses have an immune response that lasts only a few months. The same may be true with this virus. Additionally SARS CoV-2 antibody levels have been shown to decrease with time. This is a common occurrence with viral immunity and does not necessarily mean people are no longer protected, but it is possible.
  5. One antibody may not be enough. The antibody tests are to specific proteins on the virus but the immune system produces multiple different antibodies. It may be that the presence of multiple different antibodies are necessary to confer protection and this test done only identifies one. It may identify the one that is not important.

Do not take all this to mean that that there is no immunity to SARS CoV-2 after recovery from infection. It is certain that there is. This is foundational in immunology and is the basis for all vaccine effectiveness. And, while there have been rare reports of reinfection, this appears to be a rare phenomenon. The issue is using the results of the test itself in making decisions.

As of now, there are no reputable medical societies or public health institutions that recommend using antibody testing to determine if an individual is immune. This is because of all the problems listed above. There is great hope that with more research more will be known and antibody testing can be used. With time, the labs will also be able to refine their testing protocols and find the testing that is the most reliable. We’ll know which antibodies are essential and how long they confer protection. This would make antibody testing a crucial tool in fighting the virus. The problem is that these questions all take time to answer. To imagine that, since the lab spits out a number on a test result, that number is meaningful is premature.

The bottom line is that if you are making decisions about what to do based on the results of antibody testing, at best, you are wasting your time and money and, at worst, you may be putting yourself or others at risk. This, like everything else with this virus will hopefully improve with more time.

3 thoughts on “What’s the deal with antibody tests?

  1. Yours is the voice of sanity and reason within this confusing era. Our family regards your unique perspective as an ICU doctor in the eye of the storm with great respect. Thank you for your balanced thoughts in all your posts.


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