What is the Difference Between CMV IgG and IgM

The key difference between CMV IgG and IgM is that CMV IgG is a type of CMV antibody that indicates a person was infected with CMV at some time during their life, while CMV IgM is a type of CMV antibody that indicates a primary infection in combination with the presence of IgG.

Cytomegalovirus (CMV) is a common herpes virus that infects humans, but it is usually harmless. When you get this infection once, the virus remains in the body throughout the lifetime. Transmission of CMV takes place through body fluids like blood, saliva, urine, semen and breast milk. Healthy people do not show symptoms or illness. In other people, symptoms may include fever, fatigue, muscle aches, sore throat, and swollen glands. CMV infection is a concern during pregnancy since it can pass to the baby. Moreover, CMV is a cause for concern in immune-compromised people, especially those who underwent an organ, stem cell or bone marrow transplant or have AIDS. Mild CMV infections are not treated usually. However, if the symptoms arise, antiviral drugs can be taken. In order to diagnose CMV infection, serological tests (antibody testing) can be done, and they detect CMV antibodies in the blood. CMV IgM and CMV IgG are two types of CMV antibodies produced in response to a CMV infection.

CONTENTS

1. Overview and Key Difference
2. What is CMV IgG 
3. What is CMV IgM
4. Similarities – CMV IgG and IgM
5. CMV IgG vs IgM in Tabular Form
6. Summary – CMV IgG vs IgM

What is CMV IgG?

CMV IgG is one of the two types of CMV antibodies. CMV IgG appears after 1 to 2 weeks of IgM antibody detection. It shows a peak at 2 to 3 months post-infection. Then it remains detectable throughout the lifetime.

Generally, IgG levels go up during the active infection. Then it starts to stabilize as CMV infection resolves and the virus becomes inactive. A 4-fold increase in IgG between the first and second samples confirm an active infection. After a primary infection, a certain level of IgG (measurable amount) remains in our body for a lifetime in order to protect us from reinfection.

What is CMV IgM?

CMV IgM is the antibody that appears within the first 1 to 2 weeks after primary infection of CMV. Therefore, this type of antibody is produced as a first response to CMV infection. However, it is not always an indication of primary infection. It can be detected during the secondary infection as well. But positive CMV IgM tells us an indication of a recent infection. In most individuals, IgM level gradually decreases and becomes undetectable by 4 months after infection.

In some people, it may remain detectable until a year. When CMV reactivates in the body after a certain period of time, IgM reappears and comes to a detectable level. Hence, it is evident that the presence of IgM does not always indicate a primary infection.

What are the Similarities Between CMV IgG and IgM?

• CMV IgG and IgM are two types of antibodies produced by our body in response to CMV infection.
• They are used to diagnose the infection.
• The presence or absence of both these antibodies in the same sample is detected during serologic tests.

What is the Difference Between CMV IgG and IgM?

CMV IgG is an antibody produced by our body after several weeks of CMV primary infection while CMV IgM is an antibody produced by our body as the first response to the primary infection of CMV. So, this is the key difference between CMV IgG and IgM. Moreover, the presence of CMV IgG indicates that a person was infected with CMV at some time during their life, while the presence of CMV IgM together with IgG indicates the primary infection of CMV. Thus, this is another main difference between CMV IgG and IgM. Furthermore, IgG remains for the life while IgM gradually decreases and becomes undetectable after 4 months of post-infection.

The following infographic lists the differences between CMV IgG and IgM in tabular form for side by side comparison.

Summary – CMV IgG vs IgM

CMV IgG and IgM are two types of antibodies produced in our body against CMV. CMV IgM is produced as a first response to this infection. Therefore, IgM appears within the first 1 to 2 weeks after primary (new) infection. CMV IgG is produced several weeks after the primary infection. IgG levels go up during the active infection and then declines with the viral inactivation. However, a measurable amount of IgG remains throughout the lifetime in order to provide protection against CMV reinfections. The presence or absence of both types of antibodies is measured during a serological test. Thus, this is the summary of the difference between CMV IgG and IgM.

Reference:

1. “Cytomegalovirus (CMV): Symptoms, Causes, Treatment, and Prevention.” WebMD.
2. “Cytomegalovirus (CMV) Tests.” Lab Tests Online, 24 Mar. 2021.

Image Courtesy:

1. “Cytomegalovirus 01” By Transferred from en.wikipedia to Commons. from the Centers for Disease Control and Prevention’s Public Health Image Library (PHIL) (Public Domain) via Commons Wikimedia
2. “IgM scheme” By Artur Jan Fijałkowski (CC BY-SA 2.5) via Commons Wikimedia