Understanding a Rubella IgG Level of 36.9 IU/mL
A rubella IgG level of 36.9 IU/mL indicates protective immunity against rubella infection, meaning the patient is immune and protected from developing rubella disease, including during pregnancy. 1, 2
Interpretation of the Result
Any antibody level above the standard positive cutoff value (typically 10 IU/mL) is considered evidence of immunity. 1, 2
A level of 36.9 IU/mL falls well above the protective threshold and indicates robust immunity, either from prior natural infection or vaccination. 1
This level provides protection against both clinical rubella disease and viremia (virus in the bloodstream). 1
Clinical Significance for Pregnancy
For pregnant women or those planning pregnancy, this level provides protection against congenital rubella syndrome (CRS) in the fetus. 3
The risk of CRS is essentially eliminated when maternal immunity is documented with IgG levels above 10 IU/mL. 3
Even if re-exposure to rubella occurs, reinfection without clinical illness or detectable viremia may occasionally happen, but the risk for CRS among infants born to immune women is minimal. 1
Duration of Protection
Vaccine-induced rubella antibodies may decline with time, but surveillance data suggest that waning immunity with increased susceptibility to rubella disease does not occur. 1, 2
Postinfection immunity to rubella appears to be long-lasting and is probably lifelong. 1
Important Caveats
Do not confuse this with "equivocal" results (typically 5-10 IU/mL), which require different management. 3
Levels between 5-10 IU/mL are considered equivocal, and such patients should be treated as susceptible unless they have documented evidence of adequate vaccination. 3
Clinical diagnosis of rubella is unreliable and should never be used to assess immune status—only laboratory confirmation of IgG antibody is reliable evidence of protection. 1, 3