What is the difference between a PCR test and an Antibody test?
Click for a comparison of two methods’ application areas
What is the Covid-19 Rapid Antibody (IgM/IgG) test?
Our body builds a defence against the invading virus a certain time after encountering it (the antigen). This defence is called immunity, and antibodies are an important part of these immunity molecules.
Antibody tests (also called serology tests) show who has been infected with the virus and who previously had the disease. Our body produces certain antibodies as a defence against diseases. Antibody tests show whether we carry the virus and whether we previously had the disease by searching for the antibodies developed by the body against the virus. Covid-19, also known as the coronavirus, is one of the diseases against which our body produces its own specific antibody in response.
In its simplest form, rapid diagnostic tests are can be performed anywhere: With the help of a needle pricked in the tip of the finger, as the diabetics do daily, the antibodies contained in the blood dripped on the test cassette react with the isolated virus in the test kit and certain colours appear in the cassette line as a result of the chemical reaction. In coronavirus rapid diagnostic tests, the reaction on the cassette takes place in 10 or 20 minutes.
Rapid diagnostic tests measure antibodies, the defence mechanism developed by our body against the virus. There are two types of antibodies measured in such diseases:
1- IgM Antibodies: The first type of antibody our body produces as a result of infection is IgM antibodies. Within a few days after being infected, the IgM level reaches its peak. But IgM is a general fighter and our body essentially produces a second type of antibody so that we can target and destroy a particular virus, which is Immunoglobulin G.
2- IgG (Immunoglobulin G) Antibodies: IgG antibodies recognize the virus and know specifically how to fight it. The level of IgM antibodies declines after a certain period of time, leaving their place to IgG antibodies. Therefore, even after the disease has passed, IgG antibodies remain in the body and fight the virus again in any future encounter with the disease. In short, IgG antibodies are our body's memory that recognizes its enemy. IgG antibody levels reach their peak 28 days after infection and remain in the body for a long time.
Five days after a viral infection, our body develops certain antibodies, which in turn bind to the proteins that make up the SARS-CoV-2 virus (coronavirus) and fight them. The first antibody produced in this process is immunoglobulin M (IgM). IgM antibodies are short-lived and remain in blood for several weeks. Our immune system refines our antibodies and soon they produce the immunoglobulin G (IgG) antibody which works by locking on the target in the fight against the disease. IgG antibodies measured by antibody tests continue to live in blood, sometimes for years and sometimes for the whole life. While the length of time they live in blood is variable, antibodies formed against the SARS disease, a member of the previous coronavirus family, have been shown to provide immunity for 3 years. From this point of view, we can detect if we previously had the disease for several years after the disease thanks to the Covid-19 rapid diagnostic tests.
What is the Covid-19 PCR test?
Real Time-PCR (Polymerase Chain Reaction) usually indicates whether a specific virus is present in our body. In these tests, the genetic material contained in the sample taken from our body is replicated by use of a special method, which in turn enables the detection of viruses. Therefore, the PCR is known as the most sensitive method in the detection of viral infections (such as HIV, HCV and HBV). However, with the PCR tests, we can only detect a virus during the time it is present in the body and it cannot show whether the tested person previously had the disease. For the latter, we need to resort to the antibody tests.