From the Guidelines
A Rubella IgG level of 9 is generally considered to indicate some level of immunity, although it falls within an equivocal range. Most laboratories consider Rubella IgG levels above 10 IU/mL as positive (immune), levels below 5 IU/mL as negative (not immune), and levels between 5-9.9 IU/mL as equivocal or borderline 1. With a level of 9, you are in the upper end of this equivocal range, which generally indicates some immunity, though not as definitively as a level above 10. Key points to consider include:
- The importance of rubella immunity, especially for women of childbearing age, due to the risk of congenital rubella syndrome if infected during pregnancy 1.
- The recommendation for women of childbearing age to have definitive evidence of rubella immunity, which can be through vaccination or laboratory evidence 1. If you are concerned about your immunity status, particularly if you are a woman planning pregnancy, you might consider discussing with your healthcare provider about receiving an MMR (measles, mumps, rubella) booster vaccination. The IgG antibody test measures your long-term immunity, which can develop either from previous vaccination or from having had the infection. Given the potential risks associated with rubella infection during pregnancy, it's crucial to prioritize immunity, especially in women of childbearing age, to prevent congenital rubella syndrome.
From the Research
Rubella IgG Level Interpretation
- A Rubella IgG level of 9 is considered low, and its implication on immunity is not straightforward 2, 3, 4.
- Studies suggest that the current thresholds for immunity may not accurately reflect protective immunity, and lower antibody levels may still be protective 2, 4.
- The ability to determine an individual's susceptibility to infection relies heavily on the assay used and the ability to correlate results to a clinical interpretation 2.
Immunity Thresholds
- One study found that individuals with rubella-specific ELISA IgG titers <10 IU/mL were considered seronegative, suggesting a lack of protection against rubella 3.
- Another study defined the concentration of anti-rubella virus antibodies discriminating nonimmune from immune persons as <15 IU/mL by ELISA 4.
- However, it is noted that thresholds for immunity <15 IU/mL entail the risk of withholding rubella vaccination from susceptible persons 4.
Factors Influencing Immunity
- Humoral and cell-mediated immune responses contribute to protection from infection, and antibody screening assays may under-estimate immunity in some populations 2.
- The frequencies of rubella-specific memory B cells were modestly associated with antibody titers, suggesting the importance of inherent biologic and immune factors for the generation and maintenance of rubella-vaccine-induced humoral immune responses 3.
- Standardization of rubella immunoassays is not effective, leading to misinterpretation of results and potential adverse clinical outcomes 5.