PCR, Antigen & Antibody Tests

PCR, Antigen & Antibody Tests – What are the differences

Testing for COVID-19. There are many kinds of COVID-19 tests (PCR, Antigen, Antibody) that are available on the market today, so how do you choose. In general, there are three categories of testing.

The first is identifying whether the actual COVID-19 virus genetic material exists. This is called a NAAT (Nucleic Acid Amplification Test) or PCR test, whereby the lab looks for the genetic material of the virus itself.

The second type is the Antigen test. This type of test identifies the outer proteins of the viral shell (envelope).

The third type of test is Antibody testing. This test looks for antibodies that are specific to the outer portion of the virus, through blood testing. It shows whether an individual has developed immunity against the COVID-19 virus. Typically, you can take a blood test called IgM test to detect your first immune response after 10 days of infection. The IgG test, on the other hand, is another immune response that is more detectable after 2-3weeks of infection.

PCR, Antigen & Antibody Tests – Accuracy of Testing

The PCR testing which is the NAAT testing is the most sensitive one. This test requires a sophisticated laboratory setting which is why it may take a longer time to produce the result. 

The Antigen testing that exists now in the market is what we call RTK tests. These tests look for the antigen on the outer surface of the virus itself. They can be done anywhere without an avant-garde laboratory setting. They are not as accurate as of the PCR testing, but they are important tools in addressing the COVID-19 pandemic. 

PCR, Antigen & Antibody Tests – PCR Testing

PCR is a molecular testing method that analyses a short sequence of DNA. It can detect even low levels of genetic material, making them highly sensitive tests.

PCR remains the gold standard used to diagnose a COVID-19 infection. This test detects the genetic material or nucleic acid present inside a SARS-CoV virus particle. In addition, it also does not require additional confirmatory tests.

PCR, Antigen & Antibody Tests – Antigen Testing

Proteins, peptides, and polysaccharides, for instance, are all compositions of an antigen. Any portion of bacteria, the surface protein, capsule, toxins, and cell wall, can all serve as antigens. An antigen test, therefore, detects one or more specific proteins.

COVID-19 antigen tests can detect proteins in the SARS-CoV-2 virus. These tests are highly specific but less sensitive than molecular tests. Above all, they can be produced at a lower cost and scaled for a larger group of individuals. COVID-19 antigen tests are also often referred to as “rapid” as they can provide results in a shorter time frame.

PCR, Antigen & Antibody Tests – Antibody Testing 

After an infection or vaccination, your body produces proteins called antibodies. It may take weeks to start making antibodies the first time you have a virus. In other words, antibody (serology) tests look for specific antibodies in your blood to determine if you had a past infection with a specific virus. 

The least commonly used method for COVID-19 detection is this test. An antibody test may not show you have an infection as it can take 1-3 weeks to make antibodies. Similarly, an ongoing COVID-19 infection should not use this test as a diagnostic tool. Since COVID-19 is a new disease, it is unsure if the antibodies can protect you from future infections, or for how long the protection might last. 




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