What does a positive Cytomegalovirus (CMV) Immunoglobulin G (IgG) result indicate and how is it managed?

Interpretation and Management of Positive CMV IgG Results

A positive Cytomegalovirus (CMV) Immunoglobulin G (IgG) result indicates past exposure to CMV and the development of immunity, not an active infection. No specific management is required for an isolated positive CMV IgG result in immunocompetent individuals as it simply reflects prior infection and established immunity. 1

Diagnostic Significance of CMV IgG

• A positive CMV IgG test alone indicates past exposure to CMV and the development of immunity against the virus 1
• Over 90% of the normal adult population has IgG class antibodies to various viral antigens, including CMV 1
• CMV IgG antibodies typically persist for life after the initial infection 1

Clinical Interpretation Algorithm

For Immunocompetent Individuals:

1. Positive CMV IgG only (IgM negative):

   • Indicates past CMV infection with established immunity 1
   • No further testing or treatment required 1
   • No clinical significance in most cases 1

2. Positive CMV IgG with positive IgM:

   • May indicate recent primary infection, reactivation, or false-positive IgM 2
   • IgG avidity testing should be performed to differentiate between recent and past infection 3
   • Low avidity = recent primary infection (within past 3-4 months) 3
   • High avidity = past infection (>3-4 months ago) 3

For Special Populations:

1. Pregnant women:

   • Positive CMV IgG alone indicates immunity and low risk of congenital CMV 1
   • If both IgG and IgM are positive, IgG avidity testing is essential 1
   • The positive predictive value of CMV IgM is significantly lower in asymptomatic pregnant women (16.4%) compared to pregnant women with ultrasound abnormalities (36.7%) 3

2. Transplant recipients:

   • CMV IgG status of both donor and recipient is critical for risk assessment 1
   • CMV viral load monitoring by nucleic acid amplification test (NAAT) is recommended rather than relying on serology 1

Important Clinical Considerations

• False-positive CMV IgM results can occur in patients with Epstein-Barr virus (EBV) infection or other conditions causing immune system activation 1, 4
• Different laboratory assays for CMV IgG may yield different titer values, so results should be interpreted in the context of the specific assay used 5, 6
• In immunocompromised patients with suspected CMV disease, CMV viral load testing is more clinically relevant than antibody testing 1
• In patients with inflammatory bowel disease, particularly ulcerative colitis resistant to immunosuppressants, CMV testing should be considered as CMV is associated with adverse outcomes 1

Common Pitfalls to Avoid

• Misinterpreting a positive CMV IgG as evidence of active infection 1
• Failing to perform IgG avidity testing when both IgG and IgM are positive, especially in pregnant women 3
• Relying solely on serology for diagnosis of active CMV disease in immunocompromised patients instead of viral load testing or tissue diagnosis 1
• Overlooking the possibility of false-positive CMV IgM results in patients with acute EBV infection 4