Immunoglobulin G (IgG) and immunoglobulin M (IgM) are antibodies that the body produces when it comes in contact with a foreign, invading microorganism. The body produces these antibodies to promote the elimination of bacteria, viruses, parasites and fungi, as well as toxins produced by these microorganisms.
IgG and IgM can help in the diagnosis of various diseases, and can play an important role in evaluating the body's immune response to an infection.
Depending on the test that the doctor orders, it is possible to know whether or not these immunoglobulins are actively circulating in the blood. They can inform the doctor whether the patient is currently infected or has previously come in contact with the infectious agent.
What is the difference between IgM and IgG?
IgM and IgG are proteins that the body produces to combat infectious agents and their toxins. They play complementary roles to each other in the immune system:
- IgM: This is the first antibody to be produced when there is an infection. It is considered to be a marker of the acute phase of an infection. IgM helps to signal the immune system that an infection is occurring to promote other defense mechanisms to spring into action.
- IgG: This antibody is produced a little later, but still in the acute phase of the infection. It is produced depending on the invading microorganism and is considered to be more specific. It also remains for longer in the blood to help protect the body from future infections by the same microorganism.
IgG is also produced in the body with vaccines in order to protect the body from specific infectious agents.
When they're ordered
The IgG and IgM test is used to detect the stage of various diseases, such as toxoplasmosis, rubella, cytomegalovirus infection or COVID-19.
When a new infection occurs, the first antibodies produced are IgM, which decrease as the infection becomes more controlled. This then gives way to IgG production, which remain for the rest of your life.
Interpreting results
In general, the IgG and IgM measurement results can be interpreted according to the following table:
What do IgM and IgG reactive for COVID-19 mean?
If the rapid COVID-19 test shows a postivie IgM and IgG result, it means that the patient is infected with COVID-19. A positive IgG indicates that the patient is entering a more chronic phase of the infection, and it is common for the person to no longer have active symptoms of infection.
If only IgM was positive, it is a sign that the patient was recently infected, or that they were infected a few days ago and that the immune system has started to fight the virus. It is important to follow the doctor's recommendations to prevent transmission of the disease.
If only IgG was positive, it means that the person was recently infected and that they are no longer in the active phase of the disease. A positive IgG means the patient can no longer transmit the virus, and it is common for IgG to remain positive a few weeks after infection.
IgG and IgM tests in pregnancy
During pregnancy, the doctor may perform some blood tests to identify infections that the woman has had and to assess her immune status. This can be done by measuring IgG and IgM antibodies for specific infectious agents.
There are 5 infections that, if they remain during pregnancy, can have a high risk of transmission to the fetus: toxoplasmosis, syphilis, rubella, herpes simplex and cytomegalovirus. They can be even more serious when the mother does not have antibodies for these viruses and acquires them during pregnancy.
Therefore, it is very important to get vaccinated against rubella about a month before pregnancy and to have a blood test in order to treat other infections in advance.