Why You Are More Likely to Get a False Negative Than A False Positive

Antibody tests like the name suggests, test for antibodies not viruses; so our COVID-19 Antibody tests don’t look for the presence of the coronavirus. Instead, they find the proteins, or antibodies, that our bodies’ immune systems makes in response to COVID-19.

Our COVID-19 Antibody tests look for two kinds of antibodies that our immune system produces in response to the coronavirus:

1. IgM antibodies

These are short-lived antibodies that our body makes when we are fighting off the COVID-19 infection. These antibodies normally appear from 7 day into fighting off the virus. If you test positive for this antibody it means that you are a new COVID-19 infection and you are contagious for the virus.

These antibodies only stay in your body for a short time and usually disappear a few weeks after your infection. That is why we can use this antibody to pick up if you may be infected with COVID-19. But that is also why it is recommended that should we pick up the IgM antibody you should also use a PCR COVID (infection) test to confirm your infection.

2. IgG antibodies

The presence of IgG antibodies on your test can tell you if your immune system has ever had to fight off COVID-19. These antibodies usually appear in your blood 2 weeks after you recover from the virus.

IgG antibodies stay in your body a long time (sometimes for a lifetime) and help give you immunity against catching the virus again. If you test positive for these antibodies, not only will you know for certain that you had the virus but you will also know that you have some protection against catching the virus again.

To do an antibody test for COVID-19 with Epicentre, you will need to book a test online. You will then drive to our branch.

We will have a nurse clean your finger with an alcohol swab. We will then use a new lancet to make a small prick in your finger. A pipit will be used to draw a small sample of your blood. This sample will then be placed into the circular sample deposit site of the Orient Gene COVID19 IgG/IgM Rapid Test Cassette.

Our nurses are very gentle and whilst the test will be over quickly we will do our best to make you feel calm and safe during the entire process.

You will then wait 10 minutes while your test ‘loads’ your results. After which we will share your result with you.

Having an antibody test is helpful if:

• You had symptoms of COVID-19 in the past but weren’t tested
• Your doctor thinks you may have the novel coronavirus and started symptoms more than 3 days ago
• You have been in close contact with an individual suspected of or confirmed to have COVID-19 and you want to have a quick test done to check your status; or
• You have recovered from COVID-19 2 want to check your possible immunity

Rather get a PCR test if:

• You are looking to get a test done for an official purpose such as leaving the country, having a medical procedure or flight – as this method of testing has not yet been approved for these purposes
• You have been exposed to COVID-19 and started symptoms less than 3 days ago

If you are getting your test done to confirm an infection you should test for COVID-19 7days and onwards after you were exposed to the virus; as you can see on the graph the IgM becomes detectable from the 7th day until the 21st day

If you are testing to confirm your possible immunity or to check if you had the virus in the past, you can test at any time after your infection is complete.

The Orient Gene COVID-19 IgG/IgM Rapid Test Cassette.

This is the first COVID-19 antibody test that has been approved for use in South Africa. The specificity of this test is 100%, and it has a sensitivity of 95.8% for samples collected 10 days or more after the onset of symptoms or a positive PCR (nasal test) result (McAdam, 2020).

The accuracy of a test is measured in ‘sensitivity’ and ‘specificity’.

• Sensitivity
  • = how well does the test pick up the presence of even the smallest amount of COVID-19 antibodies in the blood
  • Basically if you’ve had COVID-19 in the past can this test pick it up?
• Specificity
  • = will it make mistakes and think I’ve had COVID-19 when I’ve really had another virus that looks like COVID-19
  • Basically if I haven’t had COVID-19, will it pick up this imposter and give you a negative test?

More info can be found here.

It’s a lot easier for scientists to make tests that have a better ‘specificity’ than ‘sensitivity’, so you are more likely to get a false negative (think you haven’t had COVID-19) than you are to get a false positive (think you have had COVID-19 when you haven’t).

You cannot have COVID-19 antibodies without having a COVID-19 infection. You may have been unaware of a COVID-19 infection because it was asymptomatic (without symptoms). Likewise, you also have a very small chance of having a false negative test on a Rapid COVID-19 Antibody test, but this does not mean you have these antibodies.

The specificity =98.7% accurate and the sensitivity = 91.4% accurate

The Healgen Coronavirus Ag Antigen Rapid Test

This COVID-19 Antigen test that has been approved for use in South Africa, Germany, the USA and by the UK. The accuracy of this test is 96.3%, and it has a high sensitivity and specificity. It is also CE certified.

For 20 years Epicentre has been fighting South African’s infectious diseases, and now we’re taking on COVID-19! We are a company founded on a vision, ending disease in South Africa! So we believe in making an IMPACT.

We are an independent organization that is committed to creating a positive impact on health & wellness for all in South Africa.

We want to close the gap between unscreened, undiagnosed, and uncontrolled HIV & COVID-19 infections as well as other chronic diseases for all South Africans.

By booking your tests with Epicentre you are supporting a real local company that has worked for 20 years in all 9 provinces, from Pollsmoor prison to Constantia; & you’re getting a gold standard service that experts trust!

You can get COVID-19 tested by our COVID-19 testing angels at our Wynberg (CT), Randburg (JHB) or Hillcrest (DUR) branches.

You can learn more on our articles on our other branches at:

• How to get COVID-19 tested in Hillcrest (DUR)
• How to get COVID-19 tested in Wynberg (CT)
• How to get COVID-19 tested in Randburg (JHB)