Clinical Lab Handbook

Container/Tube: SST

Alternate Container: Red Top

Specimen Volume: 2.5 mL

Collection Instructions: Allow specimen to clot for 30 minutes. Spin specimen in centrifuge.

Samples collected in SST collection tubes should be separated from the gel within 24 hours.

Chemiluminescence Immunoassay

An immunometric immunoassay technique is used, which involves the reaction of anti-rubella IgG present in the sample with rubella antigen coated onto the wells. After a wash step a horseradish peroxidase (HRP)-labeled antibody conjugate (mouse monoclonal anti-human IgG) is added and this complexes with bound anti-rubella IgG. Unbound materials are removed by washing.

The bound HRP conjugate is measured by a luminescent reaction. A reagent containing luminogenic substrates (a luminol derivative and a peracid salt) and an electron transfer agent, is added to the wells. The HRP in the bound conjugate catalyzes the oxidation of the luminol derivative, producing light. The electron transfer agent (a substituted acetanilide) increases the level of light produced and prolongs its emission. The light signals are read by the system. The amount of HRP conjugate bound is directly proportional to the concentration of anti-rubella IgG present.

Acute rubella viral infection is usually a mild, self limited, benign disease of short duration with symptoms that include low‑grade fever and a rash. However infection of the fetus during the first trimester of pregnancy may result in severe congenital abnormalities (congenital rubella syndrome). IgM antibodies to the virus appear and decrease rapidly within 4 to 5 weeks after the onset of symptoms, but IgG antibodies usually persist for life. Rubella tests may be used to define immune status and to determine the need for vaccination, to evaluate vaccine efficacy and as an aid to the diagnosis of recent infection. The patient groups normally tested are women of childbearing age, pregnant women or healthcare workers who may have close contact with a confirmed rubella case or have the clinical indicators of rubella viral infection.

Limitations:Heterophilic antibodies in the serum or plasma of certain individuals are known to cause interference with immunoassays. These antibodies may be present in blood samples from individuals regularly exposed to animals or who have been treated with animal serum products. Results, which are inconsistent with clinical observations indicate the need for additional testing.

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