What is the purpose of Rubella (German Measles) titration and when is it recommended?

Rubella Titration: Purpose and Clinical Indications

Rubella titration (serologic testing for rubella IgG antibodies) serves to determine immunity status, with critical importance for women of childbearing age to prevent congenital rubella syndrome (CRS), and is recommended for prenatal screening, healthcare workers, and persons with uncertain vaccination history. 1

Primary Purpose of Rubella Serologic Testing

The fundamental goal is to identify susceptible individuals who lack immunity and require vaccination, particularly because:

• Clinical diagnosis of rubella is unreliable and should never be used to assess immune status, as many rash illnesses mimic rubella and many rubella infections are subclinical 1
• The only reliable evidence of previous rubella infection or immunity is the presence of serum rubella IgG antibodies 1
• Any antibody level above the standard positive cutoff value of a licensed assay constitutes evidence of immunity 1

Critical Populations Requiring Rubella Titration

Women of Childbearing Age (Highest Priority)

All women of childbearing age should have rubella immunity routinely determined, regardless of birth year, due to the devastating consequences of CRS 1:

• Birth before 1957 does NOT provide acceptable evidence of rubella immunity for women who could become pregnant, as it only provides presumptive evidence 1
• Rubella infection during the first 12 weeks of pregnancy results in congenital infection and/or miscarriage in 80-90% of cases 2, 3
• Prenatal serologic screening should be performed routinely, and laboratories should retain specimens until delivery for potential retesting 1
• A negative rubella IgG test indicates susceptibility and requires postpartum vaccination 4

Healthcare Workers and High-Risk Occupational Groups

Healthcare workers require documentation of immunity because:

• They face occupational exposure risk and can transmit infection to vulnerable pregnant patients 1, 5
• One dose of MMR vaccine or laboratory evidence of immunity is required 1
• During rubella outbreaks, susceptible personnel should be vaccinated and removed from high-risk areas until immune 5

Other Populations Requiring Testing

• Persons with equivocal serologic results should be considered susceptible unless subsequent testing confirms immunity 1
• International travelers to endemic areas 1
• College students and persons in institutional settings 1

Testing Methodology

Modern rubella antibody testing has evolved significantly:

• Enzyme immunoassays (EIA/ELISA) are now the most commonly used commercial assays, having supplanted the older hemagglutination-inhibition (HI) test 1
• Other available methods include latex agglutination, immunofluorescence assay (IFA), passive hemagglutination, hemolysis-in-gel, and virus neutralization tests 1
• More sensitive assays can detect antibodies in persons who tested negative by older HI methods 1
• Laboratories that regularly perform antibody testing provide the most reliable results due to standardized reagents and procedures 1

Common Pitfalls and Clinical Caveats

Interpretation Issues

• Equivocal results require repeat testing or should prompt vaccination if the person lacks documented evidence of adequate vaccination 1
• Standardization of rubella IgG assays remains problematic, with different laboratories reporting varying IU/mL levels for the same sample, potentially leading to misinterpretation 6

Vaccination Considerations

• Women should be counseled to avoid pregnancy for 3-4 weeks after rubella vaccination 1, 4
• Inadvertent vaccination during pregnancy is NOT an indication for termination, as vaccine-strain virus does not cause CRS 7
• Post-infection immunity appears lifelong, though antibody levels may decline over time without increased susceptibility to disease 1

Post-Exposure Management

• Immune globulin (IG) is NOT recommended for post-exposure prophylaxis in pregnant women, as it does not prevent infection or viremia and has not been proven effective in preventing CRS 4
• Exposed pregnant women require close monitoring for symptoms and prompt IgM testing if symptoms develop 4

Diagnostic vs. Immunity Testing

It is crucial to distinguish between:

• Immunity screening (rubella IgG) to determine susceptibility and vaccination needs 1
• Acute infection diagnosis (rubella-specific IgM or paired sera showing fourfold rise in IgG), which is used to confirm active infection 1, 8