CMV IgG Avidity (CytomegaloVirus), in Visit Clinic

CMV IgG avidity measures the binding strength/maturity of IgG antibodies to cytomegalovirus. Low avidity suggests a recent primary infection (weeks to months), while high avidity indicates an older, past infection (months to years). It's used with IgM testing and clinical context—particularly in pregnancy—to help distinguish recent versus past infection and assess risk of congenital CMV.

A positive cytomegalovirus (CMV) IgG means you were exposed to CMV previously and have developed antibodies. It usually indicates past infection and likely immunity, not an active infection. To assess recent or active infection, clinicians may test CMV IgM, perform avidity testing, or PCR—especially during pregnancy or in immunocompromised people. Discuss results with your healthcare provider for next steps.

CMV IgG avidity classifies timing: low avidity suggests recent primary infection (typically within the past ~3 months); high avidity indicates an older infection and makes recent transmission unlikely. An intermediate or borderline avidity is indeterminate—repeat testing after 2–4 weeks or specialist review is recommended. Always interpret avidity alongside IgM/IgG serology and clinical context, particularly in pregnancy, to guide management.

CMV tests detect infection with cytomegalovirus. Blood assays measure IgM (suggesting recent/active infection) and IgG (past exposure). Molecular tests (PCR) or antigen assays identify viral DNA or proteins to confirm active infection and quantify viral load. Testing is used in pregnancy and immunocompromised patients to assess transmission risk and guide treatment.

CMV is usually mild or asymptomatic in healthy adults, causing flu-like symptoms. However, it can be serious for newborns—congenital CMV may cause hearing loss, developmental delays, or neurological impairment—and for immunocompromised people (transplant recipients, advanced HIV), where it can cause pneumonia, retinitis, or organ failure. Antiviral treatment and monitoring reduce complications; prevention in pregnancy and high-risk groups is important.

Yes — IgG antibodies generally show high avidity. Through affinity maturation and somatic hypermutation, IgG develops stronger binding to antigen sites, so mature IgG binds tightly even as a monomer. Early post‑infection IgG may have lower avidity that rises over weeks and helps distinguish recent from past infection. Pentameric IgM can have high overall avidity despite lower per‑site affinity.