Difference between Antibody Test IgG and IgM

The human body's normal immune response involves the production of antibodies against viruses like SARS-Cov-2, the causative agent of COVID-19. The antibodies target the virus, attacking it and ultimately killing it. Simply put, that is immunology 101. Antibodies are just big molecules of protein that defend the body from invaders. Antibodies, sometimes called immunoglobulins, are proteins made by the immune system to fight infection. They help defend us from outside substances including germs, poisons, and viruses.

Because our systems produce unique antibodies to combat various antigens, antibodies may be detected by a serology test. Unlike antibodies against other viruses like chickenpox or HIV, SARS-CoV-2 antibodies cannot be cross-protected. Therefore, a serology test (which measures antibodies) can be quite helpful in identifying a recent infection.

A serology test, on the other hand, can only identify the antibodies our systems have developed to combat the virus, rather than the virus itself. Therefore, the immune response may be broken down into phases, with IgG and IgM representing those stages respectively. They represent the two most frequent forms of antibodies in the body.

What is IgM Test?

To detect immunoglobulin M (IgM), a blood test is performed. It is the IgM antibody, the biggest of the antibodies, that appears first to fend against a new infection. The IgM is the immune system's "first line of defence" against harmful microorganisms. Depending on the nature of the infection and the site of inflammation, IgM can either play a harmful or protective function in inflammatory disorders.

Gnathostomes, or jawed vertebrates, have IgM as far back as the Devon period, more than 400 million years ago. Importantly, IgM antibodies can be detected as early as 4–7 days after an infection has begun, making an IgM antibody test a crucial diagnostic tool. IgM antibodies are rapidly depleted, hence their presence in the blood indicates a recent infection.

What is IgG Test?

A main effector molecule of the humoral response, immunoglobulin G (IgG) is the most abundant antibody in the body. About 75% of the antibodies found in human serum are IgG. During a secondary antibody reaction, IgG antibodies show off their most potent properties. In contrast to IgM antibodies, which have a low affinity and a short half-life in the bloodstream, IgG antibodies have a high binding capacity and last for a very long time.

Antibodies like this are produced between day 7 and day 14 following infection and can be detected for a long time thereafter, perhaps up to a year or more. Antibodies circulate in the bloodstream for a long time after an infection has cleared up. Since IgG antibodies take longer to develop after a viral infection or an active vaccination, testing for these antibodies is useful for gauging the extent of the immune response. IgG levels rise while IgM levels fall.

Differences: IgG Test and IgM Test

The following table highlights the major differences between IgG Test and IgM Test −


IgM Test

IgG Test


Antibodies of the IgM class are the first line of defence in the body's immune system against foreign invaders.

Immunoglobulin G (IgG) is the predominant antibody in human serum, accounting for almost 75% of all antibodies in the human body.


An IgM test can tell you if someone has recently been infected, and in some cases, if they are still sick. As IgM levels decline, IgG levels rise.

An IgG test can aid in the diagnosis of a lingering illness or the evaluation of one's immunity following a viral infection or active vaccination.


IgM antibodies are rapidly depleted, hence their presence in the blood indicates a recent infection.

Antibodies of the IgG class have a high affinity and stay in circulation for a long period compared to IgM class antibodies.


Common blood antibodies include IgG and IgM, which stand for distinct phases of the immunological response. IgG Test aids in the diagnosis of chronic infection. An IgM test, on the other hand, establishes whether a person is now infected, or if they were recently infected.