MMR Immunity Interpretation

Measles Immunity Assessment

The Centers for Disease Control and Prevention recommends that any detectable antibody level above the standard positive cutoff value of the licensed assay being used indicates immunity to measles, mumps, and rubella 1, 2, 3
Modern EIA/ELISA assays have replaced the older hemagglutination-inhibition (HI) test and are more sensitive for detecting measles antibodies 1
Persons with measles-specific antibody detectable by any serologic test are considered immune 1
Equivocal results should be treated as susceptible unless documentation of adequate vaccination or subsequent testing confirms immunity 1

The Centers for Disease Control and Prevention recommends that any antibody level above the standard positive cutoff of the licensed assay confirms immunity to rubella 2, 3, 4
The presence of serum rubella IgG is the only reliable evidence of previous rubella infection or immunity 2, 4, 5
Clinical diagnosis of rubella is unreliable and should not be used to assess immune status 2, 4, 5
Persons with equivocal serologic results should be considered susceptible unless they have evidence of adequate vaccination or subsequent testing indicates immunity 2, 4
Laboratories that regularly perform antibody testing provide the most reliable results due to standardized reagents and procedures 2, 4, 5

The Centers for Disease Control and Prevention recommends that the demonstration of mumps IgG antibody by any commonly used serologic assay is acceptable evidence of immunity to mumps 3, 4, 5
Persons with equivocal serologic test results should be considered susceptible unless they have other evidence of mumps immunity or subsequent testing indicates immunity 3, 4, 5

For measles IgM, blood should be collected during the first clinical encounter, may be detectable at rash onset, peaks at approximately 10 days after rash onset, and remains detectable for 30-60 days 6, 7
If measles IgM is not detected within the first 72 hours after rash onset, collect a second specimen at least 72 hours after rash onset 6, 7
For rubella IgM, blood can be obtained as early as 1-2 days after rash onset, peaks at approximately 7 days, and remains detectable for 4-12 weeks 6
If rubella IgM is not detectable in the first specimen, collect a second specimen 5 days after rash onset 6

False-positive IgM results can occur with parvovirus infection, acute infectious mononucleosis, cytomegalovirus, or in persons who are rheumatoid factor positive 8, 7
In low-prevalence settings, the likelihood of false-positive IgM results increases significantly 7
Confirmatory testing using the direct-capture IgM EIA method is recommended when IgM is detected in a patient with no identified source of infection and no epidemiologic linkage to a confirmed case 7

Postinfection immunity to rubella appears to be long-lasting and probably lifelong 2, 4, 5
Although vaccine-induced rubella antibody levels may decline with time, surveillance data suggest that waning immunity with increased susceptibility to rubella disease does not occur 2, 4, 5