COVID-19 Antibody Testing- What Does it Mean?

With all of the COVID-19 information swirling out there, it is hard to keep up.  Hopefully we can make it a little easier for you.



Antibodies provide a way for the body to remember how it defeated a specific viral or bacterial infection.  These pathogen-specific antibodies can attach and attack if exposed to the same pathogen again.  These antibodies lower the risk of re-infection from the specific virus or bacteria.



The Covid-19 Antibody test identifies current and past markers of an immune response to Covid-19. Unlike a Covid-19 RT PCR test, it does not detect actual viral genetic material, and is not used to test for an active infection, but rather for evidence of a past infection. It is not a nasopharyngeal swab because antibodies are found in the serum of the blood. Instead, a drop of whole blood is taken by a simple finger stick, like for a blood sugar. The entire process from finger stick to result takes about 15 minutes.

The antibody test is looking for an immunologic response to the Covid-19 virus and not to any other corona virus. It is 100% specific to Covid-19, meaning if the test is positive, there is essentially a zero chance that you have not had the virus in your system. The sensitivity is 97% for the IgG, or memory antibody and 88% sensitive for the IgM, or immediate response antibody. If your test is negative, there is still a 3% chance you may have IgG antibodies and a 12% chance you may have IgM antibodies.  This all means that you still could have been infected with the virus. You can see that a positive result is very telling and a negative result still holds a lot of value. This information coupled with an RT PCR test (test for active COVID-19 that requires a nasopharyngeal swab) and a good clinical history is an important diagnostic tool.


What does the presence of Covid-19 IgM & IgG Antibodies Mean?

IgM antibodies appear within days of the infection, but fade away after the infection goes away.

IgG antibodies show up as the body is attempting to clear the infection, usually around 10 days after symptoms begin and can provide long-term immunity. Whether it does and the exact duration of this immunity specific to Covid-19 is currently being studied.

Are the Tests Reliable & FDA Approved?

Many antibody tests have requested FDA approval. Every day, we expect to see more and more approved as the FDA wades through its backlog of both Covid-19 viral and antibody tests. Currently, and this changes daily, there are about four antibody tests on the market that have FDA approval. The others, including ours, are provided under Section C guidelines of the FDA.



These tests are used with discretion and ultimately for research at the moment. It is not for clinical decision-making, until evidence supporting use for that specific indication is available. The antibody test is a quick and useful tool for data collection, but like any test, clinical correlation is a must. All data from our tests are being contributed (non-identifiable) to the Stanford Seroprevalence Study.

What Do the Results Mean?
The most important thing to understand before you get a test is what all possible results will mean to you. There have been patients who were symptomatic and had a history of a negative RT PCR test at the time of peak symptoms. Weeks later they had an antibody test and it was positive. In this case it is highly likely that either the nasopharyngeal swab was not representative of the nasopharynx (technically difficult to achieve with a definite learning curve) or the virus had traveled deeper into the airway and the nasopharynx no longer harbored the virus.

No test on the market is 100% sensitive and specific. Because of this, there will be false negatives and false positives. False negatives tell us that you do not or did not have an infection when you actuality do or did.  False positives tell us that there is an infection when in actuality, there is not.

An IgG positive result is evidence of an immune response to a primary infection with COVID-19. Unfortunately, the relationship between IgG positivity and Covid-19 immunity has not yet been established. This means that we do not yet know whether the presence of IgG antibodies confer immunity moving forward. The other important question would be, if they do confer immunity, how long does that immunity last?  Positive results should be followed with a PCR Test to rule out active shedding of the virus in order to protect those around you.


Is It Worth It?

We believe the tests are worth it.  Every bit of data that can be provided to research is helpful in combatting and getting ahead of this aggressive and often deadly virus.  It is a new mystery to us all.  One thing we know for sure, proper sanitization, distancing, and awareness will help us all in preventing the spread of the virus.

Additionally, once we more completely understand what antibodies bring to the table, you will have a better idea of where you stand.

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