MMR IgG Testing: When Is It Necessary?
You do not need MMR IgG testing if you have documented proof of two doses of MMR vaccine given at least 28 days apart after your first birthday—this vaccination record alone is sufficient evidence of immunity and is the preferred approach. 1, 2
When Documentation of Vaccination Is Sufficient
Acceptable evidence of immunity without serologic testing includes:
- For measles and mumps: Written documentation of 2 doses of live MMR vaccine administered at least 28 days apart after the first birthday 2
- For rubella: Written documentation of 1 dose of live MMR vaccine after the first birthday 1, 2
- Birth before 1957 (except women of childbearing age for rubella, as this does not guarantee immunity and congenital rubella syndrome remains a risk) 1
If you have this documentation, no serologic testing is needed and you should not receive additional MMR vaccine. 2
When Serologic Testing IS Indicated
Order MMR IgG testing only in these specific situations:
- No documentation of vaccination available and you need proof of immunity (e.g., healthcare worker credentialing, school/employment requirements) 2
- Uncertain vaccination history or incomplete records 1
- Women planning pregnancy who lack documentation of rubella vaccination (rubella IgG specifically needed, as birth before 1957 is insufficient evidence) 1
- Healthcare facilities may consider it cost-effective to test rather than revaccinate, though this is optional 2
How to Interpret Serologic Results
If you do get tested:
- Positive IgG result: Any antibody level above the standard positive cutoff of a licensed enzyme immunoassay (EIA/ELISA) confirms immunity—no vaccination needed 1, 3, 4
- Negative or equivocal result with documented vaccination: You should still be considered immune based on your vaccination record, which supersedes the serologic result 2
- Negative or equivocal result without documented vaccination: Administer MMR vaccine and do not retest for immunity 1, 4
Critical Pitfalls to Avoid
Do not order IgM testing for immunity assessment—IgM indicates acute infection, not immunity status. Only IgG testing is appropriate for determining immune status. 4
Do not revaccinate based solely on negative serology if you have documented age-appropriate vaccination. Modern EIA testing may miss some vaccine-induced immunity that is still protective, and approximately 4-10% of vaccinated individuals may test negative despite being immune. 2, 4
Do not use older hemagglutination inhibition (HI) testing—enzyme immunoassays (EIA/ELISA) are now standard and more sensitive. 1, 4
Special Considerations for Healthcare Personnel
All healthcare workers must have documented presumptive evidence of immunity readily available. 2 For those with documented two-dose MMR vaccination who test negative or equivocal, the vaccination record takes precedence—consider them immune and do not administer additional doses based on serology alone. 2
The Bottom Line Algorithm
Do you have written documentation of 2 MMR doses ≥28 days apart after age 1? → You are immune. No testing or vaccination needed. 2
No documentation available? → Either get MMR IgG testing OR simply receive MMR vaccine (vaccination without testing is acceptable). 2
Test results negative/equivocal but you have documented vaccination? → You are still considered immune. No additional vaccine needed. 2
Test results negative/equivocal and no documented vaccination? → Give MMR vaccine. Do not retest. 1, 4