what are antibodies?
Antibodies are a key part of the immune system, the body’s natural defense system. they help protect us from harmful substances (pathogens) such as viruses, bacteria, and other foreign invaders that would otherwise cause us harm or illness.
The immune system detects proteins (antigens) on the surface of all our cells. Early in life, our immune system learns to identify our own proteins on the surface of our cells and ignores them.
When our body is exposed to a pathogen for the first time, the immune system will not recognize the new antigen on its surface and our body will launch an immune response. this involves producing antibodies that circulate in the blood and lock onto that specific foreign antigen to mark the cells as a problem to be eradicated.
what is igg antibody?
There are 5 main types of antibodies, each with its own role to play. the igg antibody is the one that marks the pathogenic cells to be destroyed.
Some of these antibodies will remain in circulation afterward, so if you are exposed to the same pathogen again, your immune system can quickly redistribute the antibodies and destroy the pathogen without making you sick. this is immunity.
Sometimes the immune system can’t retain enough of these antibodies, or none at all, so we’re at risk of re-infection.
what is the covid-19 antibody test?
the covid-19 antibody test is a blood test that looks for the igg antibody in your blood. if you were exposed to the sar cov-2 virus, which causes covid-19, your immune system should have produced igg covid-19 antibodies.
when is the best time to get a covid-19 antibody test?
Because it takes time for the immune system to develop igg antibodies, the blood test cannot be done too soon. studies tell us that more than 90% of people who have had covid-19 will have produced the igg antibody 14 days after the start of the disease.
therefore, the best time to do the igg covid-19 antibody blood test is 14-21 days after you first feel unwell. It is not yet fully known how long the igg antibody will continue to be detected in the blood because the virus has not been around long enough.
what does the test consist of?
A physiologist will take a sample of your blood from a vein in your arm, just like a normal blood test. It is a very quick and relatively painless process.
once your blood sample has been taken, it will be sent to a nuffield health pathology lab for analysis. the results will tell us if your blood sample has the covid-19 igg antibody (positive result) or not (negative result).
how accurate is the covid-19 antibody test?
the covid-19 antibody test we use at nuffield health is highly accurate and has been approved by public health england.
This test has a sensitivity of 100% (meaning the test will actually identify the covid-19 igg antibody if it is present in the blood 100% of the time) and a specificity of >99.8% (which which means that the test will correctly identify that there are no antibodies in the blood almost all the time).
understand my results
what does a positive antibody test mean?
a positive covid-19 igg antibody test means that you were previously exposed to the virus that causes covid-19 and that your immune system developed antibodies in response to it.
In most cases, exposure to the covid-19 virus would have caused symptoms of infection. however, a small percentage of the population can carry the virus and develop antibodies without developing symptoms (asymptomatic carriers). a positive result does not mean:
- now has immunity to the virus; It is not yet clear whether covid-19 igg antibodies confer lifelong immunity and there is evidence that some people develop the disease more than once
- cannot spread the virus to other people; you may have had a previous exposure, which resulted in igg antibodies, but you caught the virus again
- may ignore social distancing, good hygiene, and infection control measures.
- has not been exposed to the covid-19 virus (a true negative result)
- You have been exposed to the covid-19 virus, but your immune system has not produced antibodies in response to the virus (a false-negative result). this can happen because:
- the test was done too soon after the start of the infection (igg antibodies are produced after 14 days from the start of the infection, with optimal levels after day 21)
- your immune system responded to the covid-19 virus without producing the igg antibodies.
what should I do after receiving my result?
Whatever your covid-19 antibody result, government advice on social distancing, good hygiene with proper handwashing, infection control measures by wearing face masks and staying home unless travel is essential, they remain the same for everyone.
This is because so far there is very little evidence on whether the antibody provides immunity or protection against re-infection. Until there is a clear correlation, everyone must follow government instructions.
If you would like to book an igg covid-19 antibody test with us, find out more here.
last updated Tuesday, May 11, 2021
first published on Thursday, September 3, 2020
what does a negative antibody test mean?
a negative igg covid-19 antibody test means that your immune system has not developed antibodies in response to the virus that causes covid-19. this could be due to a few reasons: