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Test ID: RBPG    
Rubella Antibodies, IgG, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Determination of immune status to the rubella virus

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Rubella (German or 3-day measles) is a member of the togavirus family and humans remain the only natural host for this virus. Transmission is typically through inhalation of infectious aerosolized respiratory droplets and the incubation period following exposure can range from 12 to 23 days.(1) Infection is generally mild and self-limited, and is characterized by a maculopapular rash beginning on the face and spreading to the trunk and extremities, fever, malaise, and lymphadenopathy.(2)

 

Primary, in utero rubella infections can lead to severe sequelae for the fetus, particularly if infection occurs within the first 4 months of gestation. Congenital rubella syndrome is often associated with hearing loss, cardiovascular and ocular defects.(3)

 

The US 2-dose measles, mumps, rubella (MMR) vaccination program, which calls for vaccination of all children, leads to seroconversion in 95% of children following the first dose.(1) A total of 4 cases of rubella were reported to the CDC in 2011 without any cases of congenital rubella syndrome.(4) Due to the success of the national vaccination program, rubella is no longer considered endemic in the United States (cdc.gov/rubella). However, immunity may wane with age as approximately 80% to 90% of adults will show serologic evidence of immunity to rubella.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Vaccinated: positive (> or =1.0 AI)

Unvaccinated: negative (< or =0.7 AI)

Interpretation Provides information to assist in interpretation of the test results

Positive: Antibody index (AI) value > or =1.0

-The reported AI value is for reference only. This is a qualitative test and the numeric value of the AI is not indicative of the amount of antibody present. AI values above the manufacturer recommended cut-off for this assay indicate that specific antibodies were detected, suggesting prior exposure or vaccination.

-The presence of detectable IgG-class antibodies indicates immunity to the rubella virus through prior immunization or exposure. Individuals testing positive are considered immune to rubella infection.

 

Equivocal: AI value 0.8-0.9

Submit an additional sample for testing in 10 to 14 days to demonstrate IgG seroconversion if recently vaccinated or if otherwise clinically indicated.

 

Negative: AI value < or =0.7

The absence of detectable IgG-class antibodies suggests the lack of a specific immune response to immunization or no prior exposure to the rubella virus.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

IgG-class antibodies to rubella virus may be present in serum specimens from individuals who have received blood products within the past several months, but who have not been immunized or experienced past infection with this virus.

 

Serum samples drawn early during acute phase of infection may be negative for IgG-class antibodies to this virus.

 

The presence of antirubella-IgG antibodies does not exclude the possibility of a recent or ongoing infection. Testing for IgM-class antibodies to rubella should be performed at a state health laboratory or at the CDC if the clinical presentation is suggestive of acute rubella infection.

Supportive Data

To evaluate the accuracy of the BioPlex Rubella IgG multiplex flow immunoassay (MFI), 500 prospective serum samples were analyzed in a blinded fashion by the SeraQuest Rubella IgG EIA (Quest Int., Doral, FL) and the BioPlex Rubella IgG assay. Samples with discordant results after initial testing were repeated by both assays during the same freeze/thaw cycle. Further discrepancies were evaluated by the Rubella IgG VIDAS enzyme-linked fluorescent immunoassay (ELFA; bioMerieux, Inc.). The results are summarized below:

 

 

SeraQuest Rubella IgG EIA

BioPlex Rubella IgG

 

Positive

Negative

Equivocal

Positive

446

0

0

Negative

7

23

4

Equivocal

17

0

3

 

6/7 samples tested as equivocal by the VIDAS Rubella IgG ELFA.

Sensitivity: 94% (446/470); 95% Confidence Interval (95% CI): 92.5% to 96.6%

Specificity: 100% (23/23); 95% CI: 83.1% to 100%

Overall Percent Agreement: 94.4% (472/500); 95% CI: 92.0% to 96.1%

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. American Academy of Pediatrics. Rubella. In Red Book. 2012 Report of the Committee on Infectious Diseases. Edited by LK Pickering, Elk Grove Village, IL, 2012

2. Best JM: Rubella. Semin Fetal Neonatal Med 2007;12(3):182

3. Duszak RS: Congenital rubella syndrome-major review. Optometry 2009;80(1):36

4. Morbidity and Mortality Weekly Report: Notifiable Diseases and Mortality Tables 2012;61(34):466-479