What lab test indicates immunity to measles in an adult who had measles?

Measles Immunity Testing in Adults with Previous Infection

Measles IgG antibody testing is the gold standard for determining immunity status in adults who have previously had measles infection. 1

Acceptable Evidence of Measles Immunity

According to CDC and ACIP guidelines, acceptable evidence of immunity to measles includes:

1. Documentation of adequate vaccination
2. Laboratory evidence of immunity (positive measles IgG)
3. Laboratory confirmation of previous disease
4. Birth before 1957 (except for healthcare workers)
5. Documentation of physician-diagnosed measles 2, 1

Laboratory Testing for Immunity

For adults with a history of measles infection but without documentation, serologic testing is the appropriate approach:

• Measles IgG antibody test is the recommended test to confirm immunity status 1
• Any antibody level above the standard positive cutoff value of a licensed assay is considered evidence of immunity 1
• Prevaccination antibody screening is not necessary unless considered cost-effective 1

Interpretation of Test Results

• Positive IgG result: Indicates immunity to measles from previous infection or vaccination
• Negative or equivocal IgG result: Suggests lack of immunity despite reported history of disease; vaccination would be recommended

Special Considerations

Healthcare Workers

• Healthcare workers require more stringent evidence of immunity due to higher risk of exposure and transmission 2
• For healthcare workers born before 1957 (traditionally presumed immune), serologic testing may still be recommended as studies show up to 9.3% may lack immunity 2
• During the 2008 Arizona outbreak, 11% of healthcare providers born during or after 1957 without documented measles immunity were found to be seronegative 2

Limitations of Testing

• Both false-positive and false-negative results can occur with measles IgG testing 3
• The correlation between ELISA-IgG assays and the degree of protection is not always well-defined 4
• In one study, false negative rates were found to be as high as 72.5-75.6% when using post-vaccination IgM as the reference standard 4

Recommendations for Adults with History of Measles

1. First step: Obtain measles IgG antibody testing to confirm immunity status
2. If IgG positive: No further action needed, considered immune
3. If IgG negative or equivocal: Administer MMR vaccine regardless of history of disease, as clinical diagnosis may not always be accurate

During Outbreaks

• During outbreaks, do not delay vaccination for serologic screening 1
• All persons at risk should have evidence of immunity to measles, including laboratory evidence 2

Long-term Immunity

Measles antibodies typically persist for decades in individuals who have had natural infection. However, the antibody levels may decline over time, and in rare cases, reinfection can occur 1, 5.

By obtaining measles IgG testing, you can definitively establish immunity status in adults with a history of measles infection, avoiding unnecessary vaccination while ensuring adequate protection.