Antibody vs Antigen Testing for COVID-19

Ever since the emergence of the global pandemic COVID-19, testing has become crucial for diagnosing and treating the outbreak. 

In addition, the most common tests are the COVID antibody test and antigen test. But, what’s the difference between both tests? Why are they important? Read this post to find out. 

Antibodies and Antigens Explained

Let’s start with the basics. Antigens are distinct molecules that can stimulate your immune system. They are categorized into proteins, lipids, polysaccharides, and nucleic acids. 

All these antigens have unique surface features that your immune system can detect. Similarly, COVID-19 is known to possess various antigens which are visible from the surface. 

On the contrary, antibodies are molecules produced by the immune system as a defence reaction to antigens. In addition, antibodies contain sites for antigen binding called paratopes. These paratopes then bind to the surface of a given antigen called an epitope. 

This process helps in removing antigens from your body by neutralising them or tagging them for removal by other immune system arms.  

So, when you are infected with COVID-19, your body will produce antibodies that will then bind to COVID-19 antigens. As a result, experts can use antigen testing and the COVID antibody test to diagnose you with SARS-CoV-2.

What are these Tests Used for?

Antigen testing is used to search for COVID-19 antigens. If your system contains such antigens, then you have an active infection. In contrast, antibody testing looks for antibodies against COVID-19. These antibodies indicate that you have been previously exposed to the virus. 

How is an Antibody or Antigen Test Performed?

Antigen tests require a mucus sample from your nostrils or throat. The process includes inserting a swab to collect the mucus. The sample is then tested to look for specific proteins indicating the presence of SARS-CoV-2. The most common of these is the lateral flow test, which has been employed in huge numbers to test quickly and effectively for Covid.

Whereas for antibody tests, a blood sample is drawn by pricking your finger from your arm veins. Your blood is examined to search for antibodies in response to the COVID-19 infection. This test is now becoming more common as more people have had Covid and want to know if they have the antibodies in their system.

What if You Test Positive?

If you test positive for an antigen test, you have an active infection even if you do not notice any apparent symptoms. Regardless, you should isolate yourself for at least five days before you test again. 

Moreover, if you have a positive result for antibody testing, you were infected with the virus sometime before. However, antibody testing does not determine if you have an active infection. So, you can not rely on these tests to know your current infection status. 

Are You COVID-Free?

A negative antigen test shows that you are not infected with COVID-19. However, these results can be false-negative if you test too early before antigens show up. 

In contrast, if you have a negative antibody test, you have never been infected with COVID-19. But, if you take the test too soon after diagnosis or observing symptoms, you may have a false-negative result as antibodies take a few weeks to develop in your body. 

How Long Do Results Take?

The result duration for both tests varies significantly. For instance, if you have taken an antigen and your sample is sent off to the lab, you will have your result in about 24 hours or more. 

On the contrary, there is another type of antigen testing called rapid testing, which provides quick results within 20 minutes. In addition, antibody testing can take up to a day or more to show accurate results.