Rubella Antibody Test

Also Known As:  German Measles. Three-day Measles, 3-day Measles

Formal Names: Rubella Antibodies, Rubella IgG, Rubella IgM

Test Panel: TORCH profile, Toxoplasmosis , Herpes Simplex , Cytomegalovirus , syphilis , VDRL,

Why Get Tested:

• It diagnoses the rubella infection.
• It is done to find the immune status of the patient.
• It is advised in the pregnant ladies.
• It may be advised in low weight baby.

When to Get Tested:

• when a pregnant woman has symptoms of rubella, such as fever and rash.
• Prior to or at the beginning of a pregnancy to verify immunity
• when a newborn shows signs of abnormal development or birth defects that may be caused by an in utero infection.
• whenever there is need to verify a recent rubella infection or to verify immunity.

Normal Values:

• Latex agglutination method = This is rapid and convenient.
  • Normal = Negative for IgG and IgM antibodies.
  • IgG positive indicate previous exposure, or current immunization.
  • IgM positive indicate current or recent infection.
• HAI  (Hemagglutination inhibition method)
  • <1:8 = No immunity to infection.
  • >1:20 = Immunity to rubella infection.
  • The disadvantage is that it detects both IgM and IgG.
• ELISA
  • IgM = >1.1 IU/mL = Indicate  Active infection.
  • IgG = <7 IU/mL = Indicate No immunity to rubella.
  • IgG = >10 IU/mL = Indicate Immunity to rubella.
• Semiquantitative immunoassay method 
  • This is indirect enzyme labeled immunoabsorbent assay using microwells of a solid phase.

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Immunology:

• There is the formation of antibody IgM and IgG against rubella.
• If IgG and IgM are negative then the patients never suffered from rubella infection and not been vaccinated.

1. IgM appears in a few days to weeks after the onset of rubella rash.
   
   1. IgM disappears in about 6 weeks.
   2. For active disease advise IgM.
   3. To identify congenital infection advise IgM.
   4. IgM is necessary to label acute infection.
   5. IgM can not cross the placental barrier, therefore the presence of IgM in the neonatal period is diagnostic of congenital rubella syndrome. 
   6. In the newborn for the confirmation of the rubella infection, IgM will be positive at least for 6 months.
2. IgG persists at a low level and detectable for years.
   
   1. For immune status advise IgG.
      1. IgG titer of 1:8 or more indicates past infection and future protection from the rubella infection.
      2. Titers of 1:8, 1:16, 1:64 and 1:512 or greater are found in acute and past infections.
      3. To confirm acute infection, then advise IgM on the same serum sample.
   2. IgG can cross the placental barrier and enter into the fetal circulation.
3. Acquired infection:
   1. In the case of primary rubella infection, the presence of IgM and IgG antibodies are associated with the appearance of clinical signs and symptoms.
   2. IgM detectable a few days after the onset of S/S and reach a peak level at 7 to 10 days.
   3. These antibodies persist but decrease in concentration over the next 4 to 5 weeks until these antibodies are not detectable.
   4. IgG remains present and protective indefinitely.
4. Congenital infection:
   1. As IgG can cross the placental barrier so cannot distinguish in the fetal or maternal IgG antibodies in the neonatal blood.
   2. IgM testing is not valuable as it can not cross the placental barrier.
5. Diagnostic tests methodology:
   1. Latex agglutination.
   2. Hemagglutination inhibition (HAI).
   3. Passive hemagglutination  (PHA).
   4. Enzyme Immunoassay for IgM.
      1. Enzyme immunoassay for IgG.
   5. Radioimmunoassay (RIA).
   6. Fluorescent immunoassay (FIA).

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