Clinical Information

Discrimination between recent (primary) and past cytomegalovirus (CMV) infection can be an important tool in the clinical management of pregnant women. Although nearly all individuals with recent CMV infection are positive for CMV IgM, individuals with past CMV may also express CMV IgM due to long-term IgM persistence or viral reactivation; thus, detection of CMV IgM is not a reliable indicator of recent CMV infection. Measurement of CMV IgG avidity can assist in discriminating recent from past CMV infection. A low avidity index is a reliable indicator of CMV infection within the previous 6 months, a high avidity index essentially excludes the possibility that infection occurred within the previous 4 months. Avidity index values should be considered within the context of other laboratory findings and clinical signs.