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Blood Test Tracker

Measles (Rubeola) IgG

Checks for antibodies that show your body has met the measles virus, through vaccination or past infection. It is often used to check immunity.

AI-verified against cited sources. Awaiting expert reviewAlso called MeV IgG, Rubeola IgGLOINC 35275-7

What it is

IgG is the kind of antibody that stays in your blood long after your body meets a germ. Finding measles IgG means you have been exposed to the measles virus, through the MMR vaccine or an infection. Labs usually report the result as immune, equivocal or not immune. Some also print a number (an index or AU/mL), but the cutoffs differ from lab to lab, and the number is not a measure of how protected you are.

Why it matters

This test is most often used to check immunity when vaccination records are missing, for example for school, work in health care or travel. In the US, ACIP accepts documented vaccination, birth before 1957, lab-confirmed past illness or lab evidence of immunity as evidence of measles immunity. Measles spreads easily, so knowing your status helps you and the people around you.

If it’s low

A not-immune or equivocal result means no measles IgG, or too little to count, was found. It does not always mean you are unprotected. If you have documented vaccination, ACIP says that record takes precedence over a later blood test. A person with an equivocal result and no other evidence of immunity is not considered to have adequate evidence of immunity.

Common causes

  • You have not been vaccinated or infected
  • Vaccine doses that were given but are not documented
  • Antibody levels that fall below what the test can detect, years after vaccination
  • Blood drawn too soon after a vaccine dose or infection for antibodies to form
  • A weakened immune system, which can lower antibody levels

What can help

  • Look for your vaccination records from school, military service, a previous employer or your state's immunization registry
  • Ask your clinician whether an MMR vaccine dose makes sense for you

What can affect your result

  • Vaccination history: documented doses count as evidence of immunity even if a later test is negative or equivocal
  • Timing: very recent vaccination or infection can give a negative result
  • The assay: cutoffs, units and wording differ between labs
  • Immune-system conditions or treatments that lower antibody levels
  • Serum collected early in an acute infection, or soon after a vaccine dose, can be negative for IgG because the antibodies have not formed yet (Mayo Clinic Laboratories). Mayo advises sending a new sample 10 to 14 days later when an equivocal result follows a recent vaccine.
  • Antibodies from blood products received in the past several months can show up as measles IgG in someone who has not been vaccinated or infected (Mayo Clinic Laboratories).
  • Cutoffs and units (an index, antibody index or AU/mL) differ between labs and assays, so a number from one lab cannot be compared directly with another.

Antibodies take a few weeks to develop after an infection or a vaccine dose, so a very early sample can be negative.

When to talk to a clinician

Contact a clinician promptly if you have been near someone with measles and are not sure you are immune, or if you develop a fever with a rash. Call ahead so the clinic can arrange care in a way that protects others.

Questions you could ask

  • Do I need this test, or do my vaccination records already show immunity?
  • Do I have vaccination records that count as evidence of immunity?
  • Does an MMR vaccine dose make sense for me?

Questions people ask

Does 'immune' mean I'm fully protected?

Detectable measles IgG is accepted as laboratory evidence of immunity. ACIP says antibodies detectable by any commonly used test count as adequate evidence. The number itself is not a measure of how strong your protection is.

My result is negative or equivocal, but I had two MMR shots. What now?

ACIP says documented vaccination supersedes the result of a later blood test. Share your vaccination record with your clinician. They can tell you whether any other step is needed.

Why do labs print different numbers and cutoffs?

Each lab uses its own method and cutoffs, and some print an index while others print AU/mL. Mayo Clinic Laboratories notes its number is for reference only. Go by the interpretation your lab prints (immune, equivocal or not immune) rather than comparing numbers between labs.

Show the science and sources

For clinicians and researchers

Qualitative or semi-quantitative IgG immunoassay. Mayo Clinic Laboratories notes the presence of detectable IgG indicates prior exposure through infection or immunization, that individuals testing positive are considered immune, that the reported antibody index is for reference only, and that the test is qualitative, so the number does not reflect the amount of antibody. Its multiplex flow immunoassay (ROPG) calls an antibody index of 1.1 or higher positive, 0.9 to 1.0 equivocal and 0.8 or lower negative. Commercial assays report an index or arbitrary units (AU/mL) with an equivocal zone, and the cutoffs are manufacturer-specific. ACIP (MMWR 2013) accepts documented vaccination at 12 months or older, laboratory evidence of immunity, laboratory confirmation of disease, or birth before 1957 as presumptive evidence of immunity. It treats measles IgG detectable by any commonly used serologic assay as adequate laboratory evidence of immunity, and persons with an equivocal result as lacking adequate evidence of immunity. It discourages serologic screening when other acceptable evidence exists, and says documented vaccination supersedes later serologic results. It also does not recommend routine postvaccination testing. IgG alone does not date an infection. CDC lists measles-specific IgM in serum and measles RNA by RT-PCR from a respiratory specimen as the most common ways to confirm an acute infection.

LOINC 35275-7 (primary), 7962-4, 5244-9, 20479-2, 111039-4. Specimen: serum.

Sources

  1. 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)
  2. ROPG - Measles (Rubeola) Antibodies, IgG, Serum, Mayo Clinic Laboratories
  3. ROGM - Measles (Rubeola) Virus Antibody, IgM and IgG, Serum, Mayo Clinic Laboratories
  4. Clinical Overview of Measles, CDC

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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