Human CMV is a herpes virus. It is ubiquitous, species specific, and spread by close human contact. Primary infection may be acquired through different transmission routes and in different periods of life (e.g., congenital, perinatal and postnatal infections). Serologic diagnosis of CMV infection relies on the detection of IgG and IgM antibodies. CMV IgM appears within 2 " “4 weeks and persists for several weeks. In addition, CMV IGM may reappear during secondary CMV infection. CMV IgG can be detected typically after 4 weeks and persists for years to life. Unequivocal diagnosis of CMV primary infection is achieved by documenting a CMV IgG seroconversion on acute convalescent pair of serum samples.
Use
Aids in the diagnosis of mononucleosis-like illness in immunocompetent patients
Discriminates between current (IgM) and prior infections (IgG). Suspected CMV infection based on presentation in immunocompromised patients. Congenital syndrome that presents with symptoms of CMV
Interpretation
Normal range: Negative.
Serology reporting is done as qualitative (negative, equivocal or positive) based on the cutoff values established by manufacturer-specific clinical trials. A negative result, however, does not always rule out acute hCMV infection. The IgM response may not be detectable in the very early stage of the infection or if the patient is immunocompromised. If clinical exposure to hCMV is suspected despite a negative finding, a second sample should be collected and tested no <1 or 2 weeks.
Limitations
Screening of the general population should not be performed. The positive predictive value depends on the likelihood of the virus being present. Testing should only be performed on patients with clinical symptoms or when exposure is suspected. Diseases such as Epstein-Barr viral syndrome, toxoplasmosis, and hepatitis may cause symptoms similar to CMV infection and must be excluded before confirmation of diagnosis.