The Difference Between COVID-19 PCR and Antibody Tests



There are many aspects surrounding COVID-19 that have healthcare professionals and the general population scratching their heads. One of the aspects of confusion surrounding COVID-19 is testing. With all the news and information about testing, two main players have risen to the top in the great debate - Polymerase Chain Reaction (PCR) and Antibody (serology) testing. Both tests have been deemed as useful tools in the fight against COVID-19 and both tools have been criticized for their lack of capabilities. So what’s the difference between the two?


Differences

PCR tests detect the genetic information of the COVID-19 virus, which is called Ribonucleic Acid (RNA). Meaning PCR tests can detect the presence of the antigen, the substance that causes your immune system to produce antibodies to fight off the virus. Because of this, PCR tests have the capability to show if someone has the virus very early on.


In most cases, a PCR test is performed with a nasopharyngeal swab test, a.k.a nose swab test. The test requires a swab to be inserted up the nose of the individual who has COVID-like symptoms. The PCR test is then sent to a lab to be read by a machine and interpreted by a healthcare professional.


Antibody tests detect the presence of antibodies which are the specific proteins made in your body to respond to infections. Antibodies can be detected in the blood of individuals who have been infected by a virus and show an immune response to the infection. Antibody tests have been used for decades to detect viruses like herpes, mono, and Lyme disease. The tests are not meant to find the virus itself but are a practical tool for testing asymptomatic individuals (those with few or no symptoms) that are infecting others without knowing it and determining if you had COVID-19.


Broken down simply, the difference between the two is that the PCR test can detect the presence of an antigen (the toxic and foreign substance) and the antibody test detects the presence of the body’s immune response (antibodies) to the toxic and foreign substance.


Accuracy

The biggest source of contention in the COVID-19 PCR vs. Antibody debate is the ability to have a correct diagnosis determined.


When administered 3-10 days after symptoms develop, PCR tests can have an 80-85% specificity with 20-30% of false negatives occurring. It’s because of this that PCR tests are thought to be a great tool in confirming early infection but are not meant to give the final OK to send someone back into the population.


If properly administered 7-14 days after symptoms develop, Antibody tests can have a specificity close to 100%. For example, the Clarity COVIBLOCK COVID-19 IgG/IgM Test Cassette has a 98.8% specificity. With antibody tests, there is a possibility that they can produce false positives. However, in a pandemic, false positives are not as concerning as false negatives. One thing to note is that Antibody tests should not be used in the early stages of COVID-19 symptoms as the body has not built up enough antibodies to the virus yet.


The Winner

There is no clear winner in the case of PCR vs. Antibody testing. Nor, does there need to be. Timing is critical when considering which COVID-19 diagnostic to use. There is a time to have a PCR test and a time to have an Antibody test as neither one has been proven to be 100% accurate.


As always, if you have symptoms stay home, quarantine, and get tested at your earliest convenience, preferably using both methods of testing during the right time frame. Remember to consult your doctor to see what they believe may be the best course of action for you.


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