Serologic Testing: How Does Antibody Testing Work?

(Overlapping Voices)

There is a lot of misinformation and confusion out there right now.

Let's cut through the noise.

Here are some important facts.

Here is how testing for antibodies works: We take a sample of blood and load it into

an antibody test device.

In this machine, the SARS-CoV2 antibodies bind to the COVID antigen while the other

antibodies "don't bind" or "weakly bind" to the COVID antigen because they are not trained

to attack this specific virus.

Like in a dishwasher, the testing machine then washes off all the unbound or weakly

bound antibodies and looks for the remaining antibodies specific to a COVID-19 infection.

If it detects them, the machine determines that antibodies are present.

Pretty cool!

So why aren't we doing this everywhere right away?

Not so fast.

The test result may indicate that you have a specific new antibody to the virus that

causes the COVID-19 disease.

But we do NOT know yet if COVID-antibodies mean that they can protect you from infections.

Also, we could be dealing with false negatives or—maybe even worse—false positives.

False positives—the test thinks you have COVID-antibodies but, in fact, you don't—can

be the result of a number of reasons: for example, antibodies to a similar virus like

the common cold could "cross-react" to these viral antigens.

Serologic testing boils down to this: First: we must choose a good testing method—what

we call protocols or platforms—because not all tests are equal.

A bunch of false positives?

A greater risk for false negatives?

These are not numbers that will help us make the right decisions.

Then: The test results must be interpreted.

What does this mean?

We must make sense of the results carefully and proceed with caution.

They must be evaluated in the proper context by a medical professional.

Here are some of the issues that we need to consider:

In a way, we are always looking backward in time with the antibody test.

It takes time to develop antibodies while your immune system is gearing up for the fight.

We need the insights of researchers and clinical studies to make sense of the results, to sift

through the information, and to learn what these numbers really mean.

These studies are happening here at Penn right now.

Penn is running a number of clinical trials to determine whether antibodies from patients

who have recovered from COVID can help patients who are battling the disease.

Penn investigators are working to determine whether positive antibody tests indicate that

the patient’s antibodies are capable of blocking entry of the SARS-CoV-2 virus into


Penn has established a Coronavirus Research Center for translational research and biobanking

along with many other research efforts, resources, and clinical trials.

A positive antibody test does not mean you are immune yet.

It does not mean it's safe to go out or back to work.

Right now, it means that we don't yet know what it means.

All it means is that we can confirm that you have been exposed.

And that's a good place to start.