Immunoassay for the quantitative determination of IgG-antibodies against CMV
Cytomegalovirus (CMV) is a herpes virus ubiquitous in humans, and it is the leading infectious cause of congenital malformations.1 Anti-CMV IgG and IgM reactive samples may indicate an acute, recent or reactivated infection.
Since fetal symptomatic congenital infection is mostly due to intrauterine transmission following primary maternal infection, differential diagnosis of primary versus recurrent infection, unspecific IgM or persistence of CMV-specific IgM antibody is crucial for the management of the pregnancy.2 Antibodies produced at an early stage during primary response have lower antigen avidity than those produced at a later stage.2
There is currently no generally accepted therapy available3, but recent scientific evidences showed that antiviral medication can reduce the risk of vertical transmission, making the screening and treatment of cytomegalovirus in pregnancy to protect the unborn baby's health finally an available option4. The diagnosis of CMV infection usually starts with the detection of anti-CMV IgG and IgM antibodies. Seroconversion in CMV IgG shows a recent infection. The detection of CMV IgG antibodies is an indicator of a past infection. The time of infection can roughly be estimated in IgM positive patients by a CMV IgG avidity test3.
A low-avidity anti-CMV IgG detected before the 16th – 18th week of pregnancy, together with a positive anti-CMV IgM, is strong evidence of a recent primary infection, whereas a high avidity index during the first 12 – 16 weeks would be considered a good indicator of past infection.2 A high avidity result later in gestation cannot rule out a primary infection at an earlier stage of the pregnancy.2
The measured CMV IgG value of a patient’s sample can vary depending on the testing procedure used. The laboratory finding must therefore always contain a statement on the CMV IgG assay method used. CMV IgG values determined on patient samples by different testing procedures cannot be directly compared with one another and could be the cause of erroneous medical interpretation.