What does a positive Cytomegalovirus (CMV) Immunoglobulin G (IgG) result with a titer greater than 8 and a negative Immunoglobulin M (IgM) result indicate?

CMV IgG Positive (>8) with Negative IgM: Interpretation

A positive CMV IgG with a titer greater than 8 and negative IgM indicates past exposure to cytomegalovirus with established immunity—this is not an active infection and typically requires no further testing or treatment in immunocompetent individuals. 1

Clinical Significance

• The presence of IgG antibodies alone indicates past exposure to CMV, representing resolved infection with persistent immunity 1, 2
• CMV IgG antibodies remain detectable for life after primary infection 2
• Over 90% of the normal adult population has detectable IgG antibodies to CMV, reflecting the high prevalence of this virus 2
• The absence of IgM antibodies effectively rules out acute or recent primary infection 1

What This Result Does NOT Mean

• This is NOT evidence of active CMV infection 2, 3
• The patient does not require antiviral treatment based on serology alone 3
• No additional serologic testing (such as IgG avidity) is needed in immunocompetent patients 2

Population-Specific Considerations

Immunocompetent Adults

• No further action is required for asymptomatic individuals with this serologic pattern 2
• If clinical symptoms suggest active CMV disease despite negative IgM, CMV viral load testing by nucleic acid amplification test (NAAT) is more appropriate than repeat serology 2

Pregnant Women

• Positive IgG with negative IgM indicates immunity and low risk of congenital CMV transmission 2
• This pattern suggests infection occurred before the current pregnancy 1
• Routine CMV monitoring is not indicated with this serologic profile 1

Transplant Candidates

• CMV IgG seropositivity is critical for transplant risk stratification 2
• IgG-positive recipients are at risk for CMV reactivation post-transplant and require monitoring protocols 2
• CMV-negative recipients should ideally receive organs from CMV-negative donors when available 2

Immunocompromised Patients

• Serology has limited utility in diagnosing active CMV disease in immunocompromised hosts 1, 2
• CMV viral load by NAAT (quantitative PCR) is the preferred diagnostic test for suspected active infection 1, 2
• Positive IgG indicates risk for reactivation but does not confirm active disease 1

Common Diagnostic Pitfalls to Avoid

• Do not misinterpret positive IgG as evidence of current infection—this is the most common error 2, 3
• Do not order CMV IgM reflexively when IgG is already positive and the patient is asymptomatic 2
• Do not rely on serology alone to diagnose active CMV disease in immunocompromised patients; viral load testing is required 2, 3
• Be aware that false-positive CMV IgM results can occur with EBV infection or other causes of immune activation 1, 4

When Additional Testing IS Indicated

Despite negative IgM, consider further evaluation in these specific scenarios:

• Immunocompromised patients with clinical symptoms suggesting CMV disease (fever, hepatitis, pneumonitis, colitis): obtain CMV viral load by NAAT in blood 1, 2
• Transplant recipients with compatible symptoms: quantitative CMV DNA testing is standard for diagnosis and monitoring 1
• Suspected CMV end-organ disease (retinitis, colitis, encephalitis): tissue biopsy with immunohistochemistry and PCR may be required 3
• Inflammatory bowel disease patients resistant to immunosuppression: CMV testing on colonic biopsies should be considered 2

Summary Algorithm

1. IgG positive + IgM negative = Past infection with immunity 1, 2
2. Immunocompetent and asymptomatic: No further action 2
3. Pregnant: Reassure regarding low congenital CMV risk 2
4. Transplant setting: Document serostatus for risk stratification 2
5. Symptomatic immunocompromised: Obtain CMV viral load, not repeat serology 1, 2