You may have heard that there has been some expansion in the availability of COVID19 testing in Arizona recently. That includes PCR testing for the RNA of an active infection (which, if you have the symptoms, or are a front-line health worker, you should almost certainly get), and antibody tests to see if you have been exposed and developed an immune reaction to the virus.

Here’s the problem with the latter, antibody testing: the unknown error rate.

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The error rate, even if very small, makes antibody testing nearly useless, and possibly dangerous, for individuals, though still useful for population sampling.

Here’s the Pima County Health Director, Dr. Bob England, explaining why this is, even assuming a very high rate of test accuracy (which is likely an overly-optimistic assumption):

So, if your antibody test comes back positive, you could be tempted to place yourself in harm’s way due to a false confidence that you have antibodies, when, in fact, you don’t. And there is really no way to know if your test came back with a false positive.

So what is the benefit of an individual getting an anti-body test? Less than nothing.

A negative test, indicating you don’t have antibodies, doesn’t tell you anything of use.

A positive  test, indicating you DO have antibodies in your blood, has an unknown, but substantial, chance of being a false positive. Because of this, you should not change your behavior based on the result of such a test.

Even if the positive result is accurate, it is not actually known whether the presence of antibodies to the virus actually confers ANY immunity to the disease, or, if it does, to what level of exposure, or for how long.

So you really aren’t in any better position having taken an antibody test and gotten a positive than if you had never even taken the test. In fact, you might expose yourself to more risk due to false confidence if you have positive result for antibodies.

So don’t bother.

On the other hand, if a public health agency asks to test you for antibodies it could provide valuable information about community transmission to the scientists working to understand the virus. Just don’t rely on any result of such a test to influence your personal behavior.

One final reason not to seek an antibody test: there are a limited number. Every one that a member of the public uses is one that is not available for research. The antibody test won’t tell you anything useful, but could give health researchers useful data. Don’t waste tests that could be used to help understand and fight the virus as a part of vital research.

Stay safe. Physically distance. Wear protective masks. Wash frequently. And don’t bother seeking out an antibody test; only take one if you are asked to by a public health authority.

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