What does a positive result for measles (rubeola) Immunoglobulin G (IgG), rubella IgG, and mumps Antibody (AB) IgG indicate?

Interpretation of Positive Rubeola IgG, Rubella IgG, and Mumps IgG

These positive IgG results indicate immunity to measles (rubeola), rubella, and mumps, meaning the individual is protected against these diseases due to either prior vaccination or past natural infection. 1

What These Results Mean

Positive IgG antibodies for all three diseases represent acceptable laboratory evidence of immunity and no further vaccination or testing is needed. 1, 2, 3

Measles (Rubeola) IgG Positive

• Any measles IgG antibody level above the standard positive cutoff value of a licensed assay is considered evidence of immunity. 1, 4
• This result indicates the person is protected against measles and will not develop clinical disease if exposed. 4
• The positive IgG does NOT indicate current or recent infection—it reflects past exposure through vaccination or natural infection. 4

Rubella IgG Positive

• The presence of serum rubella IgG is the only reliable evidence of previous rubella infection or successful vaccination. 1
• Any antibody level above the standard positive cutoff value can be considered evidence of immunity. 1
• Postinfection immunity to rubella appears to be long-lasting and is probably lifelong. 1
• This is particularly important for women of childbearing age, as it indicates protection against congenital rubella syndrome in future pregnancies. 1

Mumps IgG Positive

• The demonstration of mumps IgG antibody by any commonly used serologic assay is acceptable evidence of mumps immunity. 1, 2
• This positive result indicates previous successful vaccination with mumps-containing vaccine or past natural mumps infection, which provides long-term immunity that is likely to be protective against clinical disease. 2
• This result does NOT indicate active or recent mumps infection—IgM testing would be needed for that diagnosis. 2

Clinical Significance and Recommendations

No further action is required based on these results. 2, 3

• These results can be documented as laboratory evidence of immunity to measles, mumps, and rubella. 2, 3
• The individual does not need additional MMR vaccination based solely on these positive IgG results. 2, 3
• During outbreaks of any of these diseases, individuals with positive IgG antibodies are generally considered protected, though breakthrough infections can occasionally occur. 2

Important Caveats

Antibody Persistence

• While antibody levels may decline over time, surveillance data suggest that waning immunity with increased susceptibility to clinical disease does not typically occur. 1, 2
• Even when antibody levels fall below detection by older tests (like hemagglutination inhibition), more sensitive enzyme immunoassays (EIAs) usually still detect protective antibodies. 1

If Symptoms Develop Despite Positive IgG

• If the patient develops symptoms suggestive of active measles, mumps, or rubella infection despite these positive IgG results, IgM antibody testing should be performed to diagnose acute infection. 2
• Viral detection methods (culture or nucleic acid amplification testing) may be necessary for diagnosis in previously vaccinated individuals. 2

Healthcare Workers

• For healthcare personnel, these positive IgG results meet the criteria for presumptive evidence of immunity when documented. 2, 3
• These results should be readily available in the healthcare worker's occupational health records. 3

Avoid Misinterpretation

• Do not confuse IgG (which indicates immunity) with IgM (which indicates recent or acute infection). 1, 2
• Clinical diagnosis of these diseases is unreliable—only serologic testing provides definitive evidence of immune status. 1