Best Test for Indicating Immunity to Measles
The most appropriate test to indicate immunity to measles is a serologic test for measles IgG antibody, with any antibody level above the standard positive cutoff value of a licensed assay considered evidence of immunity. 1
Testing Methods for Measles Immunity
Primary Testing Approach
- Measles IgG antibody testing is the gold standard for determining immunity status
- Enzyme-linked immunosorbent assay (ELISA) is the most commonly used method
- Any antibody level above the standard positive cutoff value indicates immunity 1
- No need for follow-up testing if results are positive
Interpretation of Results
- Positive IgG titer: Indicates immunity, no vaccination needed
- Negative or equivocal IgG titer: Indicates susceptibility, vaccination recommended 1
- Documentation of test results should be maintained in the patient's permanent medical record
Test Performance Considerations
Advantages of IgG Testing
- Provides definitive assessment of immunity status
- Avoids unnecessary vaccination if immunity is confirmed
- Reduces potential side effects and costs 1
- Results should be documented in the patient's permanent medical record
Limitations of Testing Methods
- Some commercial EIAs may have suboptimal sensitivity, particularly for vaccine-induced immunity 2
- EIAs may fail to detect measles antibodies in approximately 10% of healthcare workers with protective immunity as measured by more sensitive methods 2
- Plaque Reduction Neutralization (PRN) test is more sensitive but is not routinely available in clinical settings 2
Special Considerations
Timing of Testing
- Blood for serologic testing should be collected during the first clinical encounter with a person who has suspected measles 3
- For diagnostic purposes in acute cases, IgM testing is recommended, which peaks approximately 10 days after rash onset 3
False Positive Results
- As measles becomes rare, the likelihood of false positive IgM results increases 3
- False positive results have been reported with some commercial ELISA assays in persons with parvovirus infection 3
- Confirmatory testing using a sensitive and specific assay (e.g., direct-capture IgM EIA) should be considered in cases without epidemiologic linkage to confirmed cases 3
Alternative Testing Methods
- Significant rise in antibody titer between acute and convalescent-phase serum specimens can also confirm immunity 3
- Molecular characterization of measles virus isolates is useful for epidemiologic investigations but not for determining immunity 3
- Neutralization enzyme-linked immunosorbent assay (Nt-ELISA) shows similar sensitivity (88.3%) and specificity to neutralization tests 4
By using measles IgG antibody testing, clinicians can accurately determine immunity status and make appropriate vaccination decisions, ultimately reducing the risk of measles infection and its complications.