From the Guidelines
When a rubella IgG test comes back as indeterminate, it indicates antibody levels that fall within a gray zone between positive and negative results, and management typically involves considering the patient susceptible to rubella unless they have evidence of adequate vaccination or a subsequent serologic test result indicates rubella immunity.
Key Considerations
- Indeterminate results occur because antibody levels exist on a continuum, and the threshold between positive (immune) and negative (susceptible) isn't always clear-cut, particularly in cases of remote vaccination or exposure where antibody levels may have declined over time but some protection might still exist 1.
- For pregnant women with indeterminate results, consider them potentially susceptible to rubella and take appropriate precautions to avoid exposure to the virus.
- If the patient is planning pregnancy, retesting is recommended, and if results remain indeterminate or negative, rubella vaccination (MMR) should be given at least 28 days before conception, as the MMR vaccine contains live attenuated virus and is contraindicated during pregnancy.
Management Approach
- Management typically involves retesting in 2-4 weeks to determine if the result represents early seroconversion, waning immunity, or a false reaction.
- For healthcare workers or others requiring definitive immunity status, additional testing options include sending the sample to a reference laboratory for more sensitive testing or performing a rubella IgG avidity test to distinguish between recent and past infection.
- Although only one dose of rubella-containing vaccine is required as acceptable evidence of immunity to rubella, children should receive two doses of MMR vaccine, with the first dose administered routinely when the child is aged 12-15 months and the second before the child enters school (i.e., at age 4-6 years) 1.
From the Research
Rubella IgG Indeterminate Meaning
- An indeterminate Rubella IgG result indicates that the level of IgG antibodies against Rubella virus is not clearly positive or negative 2.
- This can occur when the result is near the cutoff value for a positive or negative test, and it may be necessary to repeat the test to confirm the result.
Management of Indeterminate Results
- If an indeterminate result is obtained, it may be necessary to repeat the test using a different assay or to use additional tests, such as IgM or avidity testing, to confirm the result 3.
- In some cases, an indeterminate result may indicate a recent infection or vaccination, and follow-up testing may be necessary to determine the individual's immune status 4.
- The management of indeterminate results should be guided by clinical judgment and may involve consultation with a specialist in infectious diseases or immunology.
Interpretation of Rubella IgG Results
- A positive Rubella IgG result indicates that the individual has been infected with or vaccinated against Rubella virus and has developed immunity 5.
- A negative Rubella IgG result indicates that the individual has not been infected with or vaccinated against Rubella virus and is susceptible to infection 6.
- An indeterminate result requires further evaluation and may involve additional testing or consultation with a specialist.
Clinical Significance of Rubella IgG Testing
- Rubella IgG testing is used to determine an individual's immune status and to identify those who are susceptible to infection 5.
- The test is also used to monitor the effectiveness of vaccination programs and to identify areas where additional vaccination efforts may be needed 6.
- Accurate interpretation of Rubella IgG results is critical for preventing the spread of Rubella virus and reducing the risk of congenital Rubella syndrome.