Rubella Serology IgG

Diagnostic Use

Indicates past infection or immunity to rubella, often used to assess vaccination status or prenatal immunity.

For query immune status (asymptomatic patient) = single serum or plasma for anti-rubella IgG

For query infection (symptomatic or exposed patient) = acute and convalescent serum for anti-rubella IgM and IgG (referred to Labplus).

Interpretation

Most postnatally-acquired rubella is asymptomatic. Adults generally have more severe disease than children and more often have prodromal symptoms of malaise, fever and anorexia. Classic rubella consists of low grade fever, lymphadenopathy, and rash.
Lymphadenopathy, involving the posterior cervical and occipital lymph nodes, and low grade fever appear prior to the onset of rash approximately 14 days after infection. The rash is erythematous, maculopapular and classically begins on the face, spreading down the body. Arthritis is a common complaint in adult women with rubella, affecting up to one-third.
Clinical diagnosis is unreliable because the symptoms are often fleeting and can be mimicked by other viruses. Laboratory confirmation of a suspected case should be attempted (Rubella PCR) and the case notified to the local Medical officer of Health to enable control measures to be put in place to halt a potential outbreak.

Rubella infection during pregnancy can result in foetal complications. If a pregnant woman has close contact with a confirmed case of rubella or develops a rubella-like illness, the first things to check are all earlier antenatal screening. If contact is in the 2nd or 3rd trimester and rubella IgG was detected in the 1st trimester, further investigation is not necessary. Otherwise, a serum sample should be collected as soon as possible for rubella IgM and IgG. If rubella IgM is negative and rubella IgG > 40 IU/mL, the patient has pre-existing immunity and the rash-illness is not due to rubella. While re-infection with rubella can occur, the risk of foetal abnormality is probably <5%, even in the 1st trimester. If the woman has negative rubella IgM and IgG results, serology should be repeated in 3-4 weeks or sooner if symptoms develop. If the rubella IgM is reactive, repeat serology is also needed to differentiate true infection from non-specific (false-positive) reactivity of the rubella IgM assay. The degree of reactivity of the rubella IgM and IgG assays will change over a 10-14 day period if recent rubella infection has occurred.

The risk to the foetus of primary rubella in the first 16 weeks of gestation is substantial; infection after 20 weeks carries no documented risk.

Measles-mumps-rubella (MMR) vaccine is given at 15 months and 4 years of age. Two doses are recommended because the 2 5 % who are not protected by the first dose will nearly all be protected by the second. After MMR, rash and high fever attributable to the vaccine have occurred in 1.6% and 1.4% respectively with the fevers around 10 days and the rash in the second week.

It is important to ensure that all women of childbearing age have been screened for rubella antibodies and, if not immune, vaccinated before pregnancy. If a woman has rubella antibodies less than 40 IU/mL she should be given MMR when not pregnant, unless she has already received 2 doses of a rubella-containing vaccine. Pregnancy should be avoided for 28 days after vaccination.
For further information on rubella immunisation refer to the current Immunisation handbook http://immunisation.book.health.govt.nz/18+Rubella

Rubella is a notifiable illness. Notify the Medical Officer of Health by phoning 09 623 4600.