Cytomegalovirus (CMV) IgG Avidity

The Cytomegalovirus (CMV) IgG Avidity test, also referred to as CMV antibody avidity or Anti-CMV IgG avidity, evaluates avidity in CMV IgG–positive patients to help distinguish recent primary infection from remote infection. Results assist with timing maternal infection during pregnancy to assess fetal risk and guide management decisions in transplant recipients and other immunosuppressed patients. Because IgG avidity increases as the humoral response matures, low avidity supports a recent primary infection, whereas high avidity argues against primary infection within the preceding few months.

Cytomegalovirus is a human herpesvirus that establishes lifelong latency with the potential to reactivate. Transmission occurs via saliva, urine, semen, blood, and vertically from mother to child during pregnancy, delivery, or breastfeeding. Primary infection in immunocompetent individuals is often asymptomatic or presents as a mononucleosis-like illness; in immunocompromised patients, disease may manifest as retinitis, colitis, esophagitis, or encephalitis. Maternal primary infection during gestation confers the greatest risk for congenital CMV. Affected infants may develop microcephaly, intracranial calcifications, hepatosplenomegaly, rash, neurodevelopmental impairment, and sensorineural hearing loss. After infection, CMV-specific IgG concentrations rise and persist, while IgG avidity reflects maturation of the humoral response. Low avidity is characteristic early after primary infection and typically transitions to high avidity by about three months, a pattern that supports estimation of infection timing.