The rubella IgG test is a blood test used to check whether someone has immunity to the rubella virus or is currently infected. It helps determine if the body has already produced protective antibodies or if there is an active infection.
This test is most often ordered during pregnancy as part of routine prenatal care. It’s commonly paired with the rubella IgM test, which helps distinguish between a recent infection, a past infection, or existing immunity.
Although the test is especially important during pregnancy due to the risk of transmitting rubella to the baby, it can be ordered for anyone. It’s often recommended when a person has symptoms that suggest rubella, such as a high fever, headache, or red, itchy skin spots.
What a reactive IgG result means
A reactive rubella IgG result means the person has antibodies that protect against the virus. In most cases, this is because of the rubella vaccine, which is part of the routine childhood vaccination schedule. The first dose is recommended at 12 months of age.
Reference ranges can vary between laboratories, but they generally include:
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Non-reactive or negative: below 10 IU/mL
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Indeterminate: between 10 and 15 IU/mL
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Reactive or positive: above 15 IU/mL
Although a reactive IgG result usually reflects immunity from vaccination, it may also indicate a past or recent infection. For that reason, additional testing is often needed to confirm the finding.
Testing and results
The rubella IgG test is straightforward and does not require special preparation. A blood sample is collected at the laboratory and then analyzed.
The sample is evaluated using serology techniques that measure the amount of IgG antibodies circulating in the blood. This helps determine whether the person has a past infection, an active infection, or immunity.
The rubella IgM antibody level is also typically measured. When IgG and IgM are evaluated together, the results may show:
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IgG reactive and IgM non-reactive: indicates circulating antibodies caused by vaccination or a past infection
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IgG reactive and IgM reactive: suggests a recent active infection
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IgG non-reactive and IgM non-reactive: indicates no previous exposure to the virus
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IgG non-reactive and IgM reactive: suggests the person currently has, or recently had, an acute infection
IgG and IgM are antibodies the body naturally produces in response to infection. IgM rises first and is considered a marker of early or acute infection. As the illness progresses, IgG levels increase and remain present long-term, which makes IgG a memory marker. Vaccination also increases IgG levels, helping protect the person over time