Coronavirus Testing Explained: Antibody (IgG and IgM) Testing, PCR Testing and Antigen Testing
Patients who understand the science behind testing methods are more empowered to fight the COVID-19 pandemic. More cases of the novel coronavirus (COVID-19) are projected to occur in the United States in the coming days, according to the Centers for Disease and Control (CDC). As a result of this projection, there has been a huge focus on testing but also a lot of confusion.
In this series, we will explain the different tests and testing methods available and their uses. We will also discuss how testing can provide benefits in the future that go beyond merely identifying active cases.
Three Testing Types
There are 3 main types of COVID-19 tests: The reverse transcriptase-polymerase chain reaction (RT-PCR) test, the antibody test, and the antigen rapid swab test. These 3 tests have advantages and disadvantages and are complementary to each other. The PCR test is the gold-standard test for COVID-19 infection due to its high sensitivity during the early phase of the infection, but it is time-consuming and costly to perform. The antibody test is fast to perform but has low sensitivity during the early phase of the infection. The antigen rapid swab test is relatively cheap and fast to perform when compared to the PCR test. The antigen test also has a relatively high sensitivity for the early phase of infection compared to the antibody test. Since the antigen test is a relatively new technology in COVID-19 diagnosis, the FDA has yet to approve many antigen tests compared to the PCR and antibody tests.
Antibody Tests PCR and Antigen Tests
When a person is infected with a virus for the first time, the immune system triggers the production of antibodies that are specific to that virus. These antibodies have the power to attach to the virus so that the immune system can destroy it.
However, it takes a while for the body to produce these antibodies. They may not even show up until the illness has run its course and, hence, may only be useful if the virus infects an individual again. If antibodies are present, they will be found inside plasma or blood samples.
Our COVID-19 IgG/IgM Rapid Test Cassette is an Antibody test. It detects the coronavirus antibodies that are in the bloodstream after people have become infected. It also helps determine whether a patient has protection toward COVID-19.
To conduct this test:
Collect whole blood/serum/plasma from the patient and place it in the center well of the cassette. According to the instructions on the kit, add one drop of the blood to the specimen well and add two drops of the buffer solution to the buffer well. The results will appear within 10 minutes. Any interpretation after 15 minutes is considered invalid.
The test cassette contains a conjugate pad with SARS-CoV-2 recombinant antigens, an IgG line coated with an anti-human IgM line, an IgM line coated with anti-human IgM, and a control line.
After the sample is placed inside the test cassette, the specimen will migrate by capillary action along with the cassette. If any antibodies are present they will bind to either the conjugates in the IgM anti-human line or those in the IgG anti-human line, depending on which antibodies are present. Individuals who have either IgM or IgG antibodies will have a positive test result.
To find out if an individual has COVID-19, the CDC and biotech companies have created coronavirus instant tests that can detect the genetic materials of SARS-CoV-2, the virus that causes COVID-19. The major test for this is referred to as polymerase chain reaction (PCR) testing.
Samples for PCR testing are typically collected from upper respiratory tract specimens (nasopharyngeal swab). They can also be collected from lower respiratory tract specimens, if available.
The PCR COVID-19 instant test kit has the right chemicals to work on the DNA in a real-time PCR machine. When a sample arrives at the lab, it is placed inside a PCR machine along with the chemicals from the PCR kit. The chemicals strip down the sample into RNA, and then the RNA is used to create thousands of copies of DNA.
Scientists then introduce sets of DNA fragments that naturally complement the fragments from SARS-CoV-2. If the virus is present, its genetic material will bind perfectly to the introduced DNA fragments.
PCR testing can take anywhere from a few hours to several days to process. However, the U.S. Food and Drug Administration (FDA) has been accelerating these tests by granting test kit manufacturers an emergency use authorization (EUA) to enable the delivery of results in less than an hour.
PCR tests can potentially deliver positive results in the asymptomatic period, which is also known as the incubation period. While the test takes only 60 minutes to run, it requires a lab technician to perform the prep work, and run and read the test results. This could take up to 2-3 hours.
One major limitation of the PCR test is that it can only detect the active virus. If an individual has recovered from COVID-19 and has antibodies, the PCR test will not detect the coronavirus, and neither will it verify the presence of antibodies. This is where antibody testing dominates.
Antibody and PCR tests complement each other to identify COVID-19 infected individuals, either symptomatic or asymptomatic.
The incubation, or asymptomatic stage, is based on an average of 5.1 days. While the PCR can detect the disease during this early stage in the development of COVID-19, The COVID-19 IgG/IgM Rapid Test Cassette must wait until antibodies develop.
The COVID-19 Antigen Rapid Test Swab Cassette is an in vitro immunochromatography assay that detects nucleocapsid protein antigen from the SARS-CoV-2 virus from the nasopharyngeal (NP) and nasal swab (NS) samples. The antigen test contains monoclonal antibodies directed against viral antigens that can detect the SARS-CoV-2 virus during the active phase of the infection. It is simple to perform the antigen test compared to the RT-PCR test, and technicians can potentially test millions of patients at once with the antigen test. The technology is similar to a pregnancy test and a rapid antigen test for influenza infections.
Like the RT-PCR test, the antigen test can detect the presence of the SARS-CoV-2 virus during the early phase of the infection. Similar to the antibody test, the antigen test is inexpensive and fast compared to the RT-PCR test and can test a large number of subjects at the point of care. However, the antigen test has a lower sensitivity compared to the RT-PCR test, which means the antigen test might have a higher false-negative rate than RT-PCR test (requires more studies). A negative result of the antigen test should be verified with an RT-PCR test before disease diagnosis and treatment decisions. The antigen test also does not give the immunity status of the patient, which the antibody test does. Therefore, the antigen test complements the PCR test and antibody test in the diagnosis of COVID-19 infection.
Reading of the IgM vs IgG Panels and How They Distinguish Acute vs In-Recovery States
What is the difference between IgM and IgG?
IgM antibodies IgG antibodies
IgM antibodies are the largest antibodies in the body and are typically produced first when an individual gets infected by a virus. IgM antibodies make up about 5% to 10% of all the antibodies in the body. They are found in the blood and lymph fluid.
Because the body typically produces IgM antibodies first, the IgM panel can detect the SARS-CoV-2 virus early. Therefore, IgM panels can accurately detect “acute infection.”
IgG antibodies are the smallest and most common antibodies. They make up about 75% to 80% of all the antibodies in the body. They are also the only type of antibody that can travel across the placenta from a pregnant woman to her unborn child. IgG antibodies can be found in all body fluids.
Unlike IgM antibodies, the body produces IgG antibodies much later. As a result, IgG antibodies can only be detected in the later course of the illness. Scientists use the IgG panels to detect “recent infection” or “in-recovery” states. An antibody testing with positive IgG with negative IgM results indicates that a person who has been exposed to or infected with COVID-19 and now has protection against COVID-19.
There are a few different types of results with (serological) antibody testing. 4 different possible outcomes:
- 1. Both IgM and IgG are negative: The patient has never been infected with COVID-19 or is still in the incubation period.
- 2. IgM is positive, but IgG is negative: The patient is having an early phase, active COVID-19 infection.
- 3. IgM is negative, but IgG is positive The patient has recently been infected with COVID-19 and now has protection against COVID-19.
- 4. Both IgM and IgG are positive: The body has an active COVID-19 infection and is trying to build up protection against it.
It is important to note that a positive test from both IgM and IgG panels means that the patient is still fighting infection and healthcare practitioners must follow all CDC guidelines for this patient.
The Importance of Serological Testing
Patients who test positive after serological (antibody) testing [Positive IgG but negative IgM,] have built up protection against COVID-19. Antibody tests are useful for determining which individuals can resume their normal activities due to their body’s new resistance to SARS-CoV-2.
Take healthcare workers for instance. These heroes are needed on the front lines to care for patients who are infected by COVID-19. For them to be successful at their job, they need to be healthy. Serological testing is important for this category of workers to ensure that they are protected against the virus.
The value of serological testing goes beyond just healthcare workers. It will prove beneficial for all essential workers, including law enforcement officials, grocery store cashiers, bus drivers, firefighters, delivery workers, people in the food business, security guards, and maintenance workers.