Test ID: CMG
Cytomegalovirus (CMV) Antibodies, IgG, Serum
Useful For 
Suggests clinical disorders or settings where the test may be helpful
Determining whether a patient (especially organ donors, blood donors, and prospective transplant recipients) had cytomegalovirus (CMV) infection in the past
Excluding CMV current infection (cord blood)
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Cytomegalovirus (CMV) is a significant cause of morbidity and mortality, especially in organ transplant recipients and individuals with acquired immunodeficiency syndrome (AIDS). (1,2) CMV is also responsible for congenital disease of the newborn. The most common infections with CMV in immunocompromised hosts result from reactivation of latent virus from a previous infection, transmission of the virus from a donor organ or blood product, or initial or primary contact with the virus in a seronegative patient. Infection in immunologically normal patients can cause mononucleosis similar to that produced by infection with Epstein-Barr virus (EBV).
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
<4 AU/mL (negative)
4-5 AU/mL (equivocal)
> or =6 AU/mL (positive)
A convalescent IgG antibody level of >6 AU/mL combined with a ratio of > or =2 in a paired sera (seroconversion) IgG titer indicates recent infection. The presence of only IgG antibodies generally indicates past infection with CMV.
Interpretation Provides information to assist in interpretation of the test results
Individuals with negative cytomegalovirus (CMV) IgG results are presumed to have not experienced infection with CMV and, therefore, are susceptible to primary infection.
Positive CMV IgG results indicate past or current CMV infection. Such individuals are potentially at risk of transmitting CMV infection through blood products; the likelihood of transmission by other modes is not known.
A ratio of > or =2 in paired sera (acute and convalescent) IgG values, along with a convalescent antibody level of >6, indicates a seroconversion has occurred and is indicative of a recent infection.
CMV infections are quite common. Approximately 60% to 85% of the population is believed to be infected by age 18.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Sera drawn very early in the acute stage of disease may have IgG levels <4 AU/mL.
The VIDAS cytomegalovirus (CMV) IgG assay demonstrates a linear dilution response to concentration. However, no international standard has been established.
The IgG titer of a single specimen should not be used to aid in the diagnosis of recent infection. Paired (acute and convalescent) specimens should be drawn and tested concurrently to look for seroconversion, which may be indicative of primary or recent infection, or of reactivation of a pre-existing latent process with active viral excretion.
Positive test results may not be valid in persons who have received blood transfusions or other blood products in the past several months.
Lack of a significant increase in IgG antibody level does not exclude the possibility of CMV infection.
Results must be used in conjunction with clinical symptoms and patient history.
This test should not be used as a general screen in the absence of clinical symptoms or known exposure.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Kusne S, Shapiro R, Fung J: Prevention and treatment of cytomegalovirus infection in organ transplant recipients. Transpl Infect Dis 1999;1(3):187-203
2. Rubin RH: Importance of CMV in the transplant population. Transpl Infect Dis 1999;1(1):3-7
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