There is a lot of information circulating around about Covid and Antibody screening. To help clarify misconceptions you may have read or heard, let’s take a deeper look into Covid first and then Antibody screening.
Coronaviruses didn’t just pop up recently. They are a large family of viruses that have been around for a long time. Infact, you have had one or more of them in the past year when you had cold symptoms. Seven different strains of Coronavirus can infect people. There are four that are common to us giving symptoms of cold and bronchitis.
Antibody screening has been a hot topic recently. News reports are urging everyone to be tested to see if they have been exposed to Covid-19. You may be asking yourself what is an antibody, and why would we test for it?
An antibody is a specific protein our body makes to fight infection. After you have had an infection or an immunization, you will have antibodies that will recognize that virus and help you fight it off in the future.
The same appears to be true for COVID. We believe that once you have had the illness, you will have antibodies to it to help you fight it in the future. Testing for these antibodies is called serologic (or serum) testing. The FDA has granted Emergency Use Authorization for this antibody testing and several companies have developed tests.
Sounds great right? Well yes and no. It’s complicated.
The first hurdle is that there are two main antibodies that your immune system uses to fight invaders. The first one, IgM, is created by the body within hours to days of the body recognizing an invader, and is used to fight off your first or immediate exposure. Within days to weeks of exposure, your body starts to create IgG, which functions as the immune system’s memory in case it sees that specific invader again. Doctors in the past have used the combination of these two antibodies to determine where in the course of a disease you are, and whether your body is responding appropriately. Most tests on the market today test for IgG only, which limits the information you can get from a result.
The second hurdle is that the tests are not perfect. Here is a disclaimer that Quest Diagnostics adds to the results on samples Madison Memorial Hospital sends to them:
“IgG antibodies may indicate exposure to SARS-CoV-2 (COVID-19). It usually takes at least 10 days after symptom onset for IgG to reach detectable levels. An IgG positive result may suggest an immune response to a primary infection with SARS-CoV-2, but the relationship between IgG positivity and immunity to SARS-CoV-2 has not yet been firmly established. Antibody tests have not been shown to definitively diagnose or exclude SARS-CoV-2 infection. Positive results could also be due to past or present infection with [other NONCOVID coronavirus types] … Diagnosis of COVID-19 is made by detection of SARS-CoV-2 RNA by molecular testing methods, consistent with a patient’s clinical findings.”
Let’s break down this statement for a moment. It states, “An IgG positive result MAY SUGGEST an immune response” to Covid-19. However, there has not been enough time to study the virus to determine whether the antibody provides complete immunity, or only partial immunity like in other coronaviruses or influenza. The disclaimer goes on to add, “positive results could also be due to past or present infection to” other strains of coronavirus, including those that cause the common cold.
So what does this mean? It means that if you get a positive result back, it might be true positive, meaning you had COVID 19, or it might be a false positive, meaning you had another coronavirus recently that gave you antibodies similar to the COVID 19 antibody.
Madison Memorial Hospital is currently sending COVID-19 IgG testing to Quest Diagnostics. The IgG test they run has a specificity of approximately 99%. This is good but in a population with low numbers of COVID, like Rexburg, the positive predictive value of the test is only 77%. This means that if your test comes back positive for IgG, there is a 33% chance that you are still NOT PROTECTED FROM COVID. It is very important to us that we not falsely reassure anyone.
Also, when they compared the results of this test to the nasal swab PCR test, there was a 10% discrepancy. This means that 10% of those who tested positive for COVID by PCR had a negative IgG test. This doesn’t necessarily mean the patient did not have COVID, rather this may just mean that they have not yet produced enough IgG to be detected.
So what does this all mean for you? It means that Antibody testing for COVID-19 cannot completely reassure you that you will be immune to it in the future. This is why all current COVID19 IgG tests recommend follow up molecular testing to confirm a diagnosis of COVID19.
Here at Madison Memorial, we want to focus on high quality results that make a difference in your life, at the lowest cost possible to you. To this end, our goal is to bring in testing that has some meaning to you and your provider, thus making the price you pay worth it.
Our primary goal is to obtain accurate PCR testing first so we can quickly diagnose patients with current COVID-19 disease. As with most labs in our area, we’ve found it difficult if not impossible to get access to PCR testing kits that can be used on our analyzers. Over time, our goal will be to bring in reliable IgG and IgM tests to achieve maximum confidence that you have been exposed and have some immunity to COVID.
We know the scientists and manufacturers are working hard to achieve this level of accuracy and hope this testing will be available to us shortly. Once it is available, we will verify the performance of the test to ensure that you get meaningful results. Until that time, we will do our best to meet your needs through the availability of testing at multiple reference labs.
https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html