What are CMV IgG antibodies?
CMV IgG antibodies are immunoglobulins of the type G that are formed by the body's immune system after an infection with Cytomegalovirus (CMV). CMV belongs to the herpesvirus family and is a common virus that often causes mild or no symptoms in healthy individuals. When the body is exposed to CMV, the immune system develops IgG antibodies that provide a long-term, often lifelong, immunological memory against the virus. The presence of CMV IgG in the blood therefore indicates a previous infection and immunity to CMV.
What is the function of CMV IgG in the body?
After the body has fought off a CMV infection, the initial IgM response changes to an IgG response. CMV IgG helps prevent a new CMV infection from taking hold by quickly recognizing and neutralizing the virus in the event of a possible reactivation. Since CMV can lie latent in the body and be reactivated in cases of impaired immune function, IgG plays an important role in limiting the spread and replication of the virus. In pregnant women, the presence of CMV IgG without CMV IgM is usually a sign that it is not a primary infection, which is relevant for the safety of the fetus.
Analysis of CMV IgG
A CMV IgG analysis is performed through a blood test that measures the concentration of specific antibodies against Cytomegalovirus. The test is used to determine whether an individual has previously had a CMV infection, which is particularly important before pregnancy, organ transplantation or in cases of immunosuppression. The CMV IgG analysis is often performed in combination with CMV IgM to distinguish between previous infection, ongoing primary infection or reactivation of latent virus.
The significance of CMV IgG in diagnostics
The CMV IgG analysis is used to determine previous exposure to Cytomegalovirus. A positive result means that the individual has probably had a CMV infection and has developed immunity. In most cases, this does not pose a health problem, but in immunosuppressed patients or fetuses, CMV can pose a serious risk. In transplant medicine, CMV IgG status is used to match donors and recipients. In pregnant women, the test is used to rule out primary CMV infection, which is the form that poses the greatest risk to the fetus.
CMV IgG in pregnancy
CMV infection during pregnancy can in some cases be transmitted to the fetus and cause congenital cytomegaly. If a pregnant woman has CMV IgG but not CMV IgM, this means that she has previously had CMV and the risk of primary infection during pregnancy is low. If both IgG and IgM are positive, this may indicate a recent infection, which requires further investigation, such as an avidity test for CMV IgG to assess the time of infection.
Normal values for CMV IgG
Normal values vary depending on the laboratory's reference interval and analysis method. A positive result is usually interpreted as the presence of CMV IgG above a defined threshold (e.g. >6.0 AU/mL or equivalent). A negative result means that the individual has probably not had a CMV infection. It is important to interpret the test result in relation to the patient's clinical picture and other laboratory values, especially CMV IgM and any symptomatology.
Use of CMV IgG in clinical practice
In clinical practice, the CMV IgG assay is mainly used to:
- Determine whether a patient has previously had CMV.
- Assess the risk of CMV reactivation in immunosuppressed patients.
- Perform pre-pregnancy or prenatal screening to assess the risk of congenital CMV infection.
- Match donors and recipients in connection with organ or stem cell transplantation.
The test is particularly relevant for patients with a weakened immune system (e.g. with HIV, after chemotherapy or during immunosuppressive treatment), where a previous infection can be reactivated and cause serious complications.