Rubella IgG
Shows whether you have antibodies to the rubella (German measles) virus, from vaccination or past infection. Often checked before or early in pregnancy.
AI-verified against cited sources. Awaiting expert reviewAlso called Rubella Ab IgGLOINC 5334-8
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What it is
Rubella IgG is an antibody your immune system makes after the MMR vaccine or after a rubella infection. Rubella is usually mild, but an infection during pregnancy can seriously harm a developing baby, a condition called congenital rubella syndrome. This test looks for the antibody to show whether you are likely protected. Labs print the result as immune, equivocal or non-immune, and often add a number. The number's units and cutoffs differ between labs.
Why it matters
Preventing congenital rubella syndrome is the main goal of rubella vaccination programs (CDC). This test is the usual way to check rubella immunity when vaccine records are missing, and it is common before or early in pregnancy and for healthcare workers. If you are not immune, vaccination before a pregnancy can protect you. CDC says the MMR vaccine should not be given to women known to be pregnant, and women should avoid becoming pregnant for 28 days after a dose.
If it’s low
A non-immune or equivocal result means not enough rubella IgG antibody was found for your lab to call you immune. When judging immunity, CDC treats an equivocal result as negative. Many people who were vaccinated still test low, because antibody levels fade over time and assays differ. This is not a sign of illness. If you are pregnant or planning a pregnancy, your clinician can explain what the result means for you and how to lower your chance of exposure.
Common causes
- Never vaccinated and never infected
- Antibody that has dropped below the test's cutoff since vaccination
- A weaker response to the vaccine in some people
- Differences between assays, since each lab sets its own cutoff and equivocal zone
What can help
- Find your vaccine record and bring it to your visit
- Ask your clinician whether a vaccine dose makes sense for you and when, especially if you are planning a pregnancy
- If you are pregnant, ask your care team how to avoid exposure and when vaccination could be done
If it’s high
A result at or above your lab's immune cutoff means rubella IgG antibody was found. US guidance accepts this as laboratory evidence of rubella immunity. Most labs use 10 IU/mL as the cutoff, but some print an index or use their own units, so go by the label on your report. A higher number does not necessarily mean stronger protection, and there is no need to chase a specific number.
Common causes
- Rubella vaccination (the MMR vaccine)
- A past rubella infection, including a mild one you did not notice
What can help
- Keep a copy of the result with your vaccine records for work, school, travel or pregnancy care
- If you are pregnant and you are exposed to someone with a rash illness, tell your care team, because an immune result does not replace a medical check
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 10 and above IU/mL. Source: Clinical Microbiology Reviews, MMWR Recommendations and Reports (CDC), Labcorp.
- Adults (this one applies)10 and above IU/mL
Sources: Clinical Microbiology Reviews, MMWR Recommendations and Reports (CDC), Labcorp
If this applies to you
Rubella IgG means a little more for some people. Open the one that fits you.
Trying to conceive
NICE offers a rubella immunity test to anyone trying to conceive who isn't sure they've been vaccinated, so vaccination can come first if needed. It advises avoiding pregnancy for at least 1 month after the vaccine.
What can affect your result
- Vaccination history and time since vaccination or infection
- Assay brand: cutoffs, units (IU/mL, AU/mL or an index) and the equivocal zone differ between labs
- Pregnancy: the MMR vaccine is not given during pregnancy, so a low result is handled differently
- The same sample can read very differently on different assays (2016 review)
- Assay brands are not standardized: a 2016 review found the same sample read from a negative 0.96 IU/mL to a strongly positive 67.0 IU/mL on different assays, so results from different labs cannot be compared number to number.
- A result printed as an index or in AU/mL is not the same as IU/mL and cannot be converted. Use the lab's own label and cutoffs.
- Grossly hemolyzed, lipemic or icteric samples, and samples with visible particles or heavy bacterial contamination, can be rejected (Labcorp).
The result reflects past vaccination or infection, not a current change, so there is no trend to wait for.
When to talk to a clinician
A low result is not urgent on its own, but talk with your clinician soon if you are pregnant or planning a pregnancy. If you are pregnant and develop a rash and fever, or have been around someone with rubella, contact your clinician or midwife promptly, even if you were told you were immune.
Questions you could ask
- Which cutoffs does my lab use, and does my report show the units clearly?
- Do I need this blood test if I can find my vaccine record?
- Does this result count as proof of rubella immunity for my job, school or pregnancy care?
- Do I have a vaccine record that counts as proof of immunity?
- Do I need any vaccine follow-up, and when, given any plans for pregnancy?
- If I am pregnant, how do we lower my chance of exposure?
Questions people ask
My lab shows an index, not IU/mL. How do I read it?
Some labs report an index instead of IU/mL. Labcorp, for example, calls above 0.99 immune, 0.90 to 0.99 equivocal and below 0.90 non-immune. Index values cannot be converted into IU/mL, so use the label and cutoffs printed on your own report.
I'm pregnant and my result isn't clearly immune. What happens next?
CDC says the MMR vaccine should not be given to women who are known to be pregnant. Talk with your care team about how to avoid exposure and when vaccination could be done. They can also explain what to do if you have a rash or are exposed to someone with rubella.
Does a high number mean stronger protection?
Not necessarily. Most labs use a cutoff, often 10 IU/mL, to call someone immune. A 2016 review points out that being above the cutoff does not guarantee protection and being below it does not always mean you are susceptible. The same sample can also read very differently on different assays.
Show the science and sources
For clinicians and researchers
Rubella IgG is measured by immunoassay (Labcorp uses a chemiluminescent immunoassay). Assays are calibrated to the WHO international standard (RUB-1-94) and usually report IU/mL, but a 2016 review (Dimech) found the standard is not a pure analyte and that results are not standardized between assays: the same sample read from 0.96 to 67.0 IU/mL, and some assays have no gray zone (a result of 9.9 is nonreactive and 10.1 is positive). The review states that commercial assays use 10 IU/mL as the cutoff between immune and nonimmune, and that the assumption that every result above 10 IU/mL protects and every result below it means susceptibility is not correct. Labcorp reports an index instead (non-immune below 0.90, equivocal 0.90-0.99, immune above 0.99), so this marker's IU/mL unit does not cover those results. ACIP (2013) accepts rubella-specific antibody above the assay's positive cutoff as evidence of immunity, advises against pre-vaccination screening when other acceptable evidence exists, and says women of childbearing age with 1 or 2 documented doses of a rubella-containing vaccine and IgG that is not clearly positive should get one additional dose (up to 3 doses in total). The CDC Pink Book says equivocal results should be considered negative when assessing immunity. Acute infection is confirmed by PCR, a significant rise in IgG across paired samples, or rubella IgM, and IgM is best collected about 5 days after the rash starts. IgM and IgG avidity are separate tests.
LOINC 5334-8 (primary), 8014-3, 25514-1, 20458-6. Specimen: serum.
Sources
- Standardization of Assays That Detect Anti-Rubella Virus IgG Antibodies, Clinical Microbiology Reviews (2016)
- Prevention of Measles, Rubella, Congenital Rubella Syndrome, and Mumps, 2013: Summary Recommendations of the Advisory Committee on Immunization Practices (ACIP), MMWR Recommendations and Reports (CDC) (2013)
- Rubella (Pink Book, Epidemiology and Prevention of Vaccine-Preventable Diseases), CDC
- Rubella Antibodies, IgG (test 006197), Labcorp
- LOINC codes verified with the NLM Clinical Tables LOINC search, U.S. National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.