COVID19 antibody assays detect the presence and/or amount of antibody present in blood by ELISA, which utilizes a spectrophotometry/absorbance measurement based on color change. Measurements of unknown samples are made against a standard curve generated for each run (IgG) or comparison to a reference control (IgM), with positive and negative assay controls for each run. Our neutralizing antibody assay is also an ELISA, and it measures how strongly a tiny drop of serum can block (or neutralize) binding of the virus to its receptors on human cells.
IgG and IgM are two different isotypes of antibodies that you may have developed against COVID-19. Most people who are exposed to the novel coronavirus develop IgM, IgG, or both. The IgG and IgM tests tell you if you have that kind of antibody to the virus’ spike protein, and how much you have, but it does not tell you how well those antibodies work.
Neutralizing antibodies are the most protective kind of antibodies against the SARS-CoV-2 coronavirus because they bind up the virus in the human body so that it cannot infect cells, thus providing true immunity. This test measures how well your antibodies work at neutralizing the virus, no matter what kind you have.
For the antibody assay it is 86769 x2; For neutralizing screen 86408
We are not a physician and therefore are not diagnosing anything.
However, code Z01.84 encounter for antibody response examination,
would be the code we would submit if we filed for reimbursement.
For IgG, the number is the “micrograms of antibody per milliliter of blood”. We can detect even very, very tiny amounts of antibodies. If you have at least 0.6 micrograms/ml of antibodies, then you are “positive”. Fun fact! People can have up to 1250 micrograms/ml of IgG against COVID-19; that is the upper limit of the amount that we can measure. But having a low number does not mean you aren’t protected; even people with low positive results can have very healthy amounts of Neutralizing Antibodies.
For Neutralizing Antibodies, the number is a percentage, and 20% is the cutoff value. Let us say that your Neutralizing Antibody result is 50%. That means, first, that you have Neutralizing Antibodies. The technical explanation is that a small drop of your serum has enough antibody in it to completely neutralize 50% of the virus binding in the test.
It is an extremely contagious virus, but your likelihood of being infected depends on many factors, but the main factor is viral shedding. “Viral shedding” means that the person who is infected is actively producing contagious virus particles that can infect others, whether by coughing, sneezing, shouting/singing, talking, etc… You have to be around someone when they are actively shedding the virus and either breathe it in or touch your nose/mouth/eyes to catch it. There’s no way to tell if and when someone is shedding, except if they had a positive nasal swab test, then you know they were shedding at the exact moment the swab was stuck up their nose. Some people shed a lot and these people are called “efficient spreaders” or “super spreaders” but some people don’t shed much or don’t shed for very long.
People can shed virus before they have symptoms, after symptoms have started, or even if they are asymptomatic and never get sick; doctors can’t predict who will shed and when, but they know that on average most people will shed right before they get sick and for a day or so after. It’s possible your loved one wasn’t shedding much virus, or that they weren’t shedding when you were in close proximity to them. Importantly, you are not alone, and this happens frequently. Many people have family members in the same household who do not get infected.
Good question, and there are many possible reasons why this can happen:
- Timing is important because your antibody levels in your blood are dynamic, meaning that they fluctuate up and down depending on lots of factors, like how long it’s been since you were first exposed, whether you have been re-exposed, other health factors that can cause you to begin making less antibody (immunosuppressive or anti-inflammatory meds, for instance), and even how well hydrated you are when your blood is taken. If your first and second test are a few days to a few weeks apart it is not unusual for the amount of antibodies to change. As an example, most but not all people will test lower on a second or third test and may even come back negative; this does not mean that they are unprotected or that the first test was wrong. It just means that the antibody levels changed.
- Not all antibody tests work the same way or measure the same kind of antibody in terms of “specificity”, which means the “target” of the antibody. For instance, our test measures anti-spike protein antibodies which are the most unique and specific antibodies to the coronavirus. Most people develop antibodies to the spike protein of the virus, but not everyone. So if you go to a lab that measures different antibodies (like anti-nucleocapsid or anti-envelope antibodies) then you would get a different result. As an example, LabCorp’s COVID-19 IgG test measures anti-nucleocapsid protein, and you may be positive for that and negative for anti-spike, and vice versa.
- Not all antibody tests work the same way or measure the same kind of antibody in terms of “isotype”. The isotype refers to the physical shape of the antibody protein: IgG looks like a “Y”, IgM is 5 “Y”s stuck together in a circle, and IgA looks like two “Y”s stuck together at the bottom. Tests usually measure one isotype at a time, like IgG or IgM. But some tests measure both together and in some cases all 3 isotypes at the same time (called a total antibody test). It is possible that your results could differ based on which isotype the test is measuring, and whether it is measuring 1, 2, or 3 together.
- Not all tests have the same sensitivity (ability to detect true positives) and different tests have different “cut-offs” for determining who is positive and who is not. The cutoffs for different brands of tests from other companies are different because they are all determined by clinical studies. The population of patients in our clinical validation study will not be exactly the same as the population of patients used by another company, therefore cutoffs differ. Especially if you are “on the edge” with low levels of antibodies, you may be called positive by one test and negative by a different test.
The Red Cross uses completely different tests in a tiered approach to determine if you have enough of the right kind of antibody to be a plasma donor. Even if you bring your Granger Genetics test results to the Red Cross, they will test you again with their own tests. First they will run a “quickie” test to see if you have COVID-19 antibodies, and then if you do, they will run a more in-depth and complicated test and “titer” your serum, meaning that they will dilute it down and see if the antibodies are at high enough concentrations in your serum to fight COVID-19 if your plasma were transfused to someone else.
The Red Cross has not stated which brand of antibody tests they use and therefore we do not know if they measure anti-Spike Protein antibodies like we do. Most people who test positive for IgG by Granger Genetics tests also test positive at the Red Cross, and thus far everyone who has tested positive for Neutralizing Antibodies at Granger Genetics has been asked to donate plasma by the Red Cross. So even if your IgG and neutralizing antibody tests are low positives, do not assume you won’t qualify as a plasma donor for the Red Cross. You still might!
Early on, some scientists were worried that SARS-CoV-2 would be like the common cold virus and that people would not develop lasting immunity and would catch it over and over. That is not the prevailing opinion anymore. Some people have tested positive again after negative tests, and scientists now know that the dead virus can hang out in your respiratory tract for weeks after recovery from infection and give a false positive result.
There has only been one documented case, world-wide, of a person contracting coronavirus twice. This was published in a study in Cell in August 2020. All we know is that a male in Hong Kong recovered from the Asian strain and 4.5 months later caught the European strain (confirmed through genetic testing). We have no information about the individual’s health, medicine he was taking, if he was immunocompromised, etc… Given that millions and millions of people have already had COVID-19 and there is only one documented case of re-infection to date, the odds of catching the same strain again are really low.