Laboratory Evidence of Measles Immunity According to CDC
The presence of measles IgG antibodies detected by any standard serologic assay is the laboratory study that most reliably indicates immunity to measles according to CDC guidelines. 1
Acceptable Laboratory Evidence
The CDC's Advisory Committee on Immunization Practices (ACIP) defines laboratory evidence of measles immunity as:
- Positive measles IgG antibody detected by any standard serologic test 1
- Any antibody level above the standard positive cutoff value of a licensed assay can be considered evidence of immunity 1
- Persons with positive measles IgG by any serologic test are considered immune 1
Important Caveats About Equivocal Results
Persons with "equivocal" serologic test results should be considered susceptible to measles unless they have other evidence of immunity (such as documented vaccination or birth before 1957) or subsequent testing indicates they are immune. 1
Clinical Context and Testing Considerations
Healthcare Worker Screening
During outbreak investigations, serologic testing has revealed that approximately 4-10% of healthcare personnel lack measles IgG antibodies, even among those born before 1957 who are presumed immune by age. 1 This underscores the importance of laboratory confirmation rather than relying solely on age or vaccination history.
Timing and Test Selection
- IgM antibody testing is used for acute measles diagnosis, not for determining immunity status 1
- IgM may not be detectable until at least 72 hours after rash onset with some assays 1
- IgG antibody testing is the appropriate test for determining immune status 1
Test Performance Considerations
While enzyme immunoassays (EIAs) are the most commonly used commercial assays for measles antibody detection, research has shown that some EIAs may have suboptimal sensitivity, particularly for detecting vaccine-induced immunity compared to natural infection. 2 However, CDC guidelines accept any positive result from a licensed assay as evidence of immunity. 1
Alternative Evidence of Immunity (Non-Laboratory)
While the question specifically asks about laboratory studies, CDC also accepts:
- Documentation of two doses of live measles vaccine administered on or after the first birthday 1
- Birth before 1957 (presumptive evidence) 1
However, laboratory confirmation with measles IgG remains the definitive serologic marker when documentation is unavailable or immunity status needs verification. 1