Rubella – Diagnostic Serology

Testing Indications

When Rubella (German Measles) infection is suspected-Contact your local Public Health Laboratory to ensure that appropriate testing is being requested and also contact your local Public Health Unit to inform them of all possible or suspect cases of rubella.

When Rubella infection is suspected, in addition to collection of serology samples, also collect and submit samples for the detection of Rubella virus by RT-PCR. Refer to the test information sheet Rubella – Diagnostic RT-PCR for specimen collection and testing information.

For Immune Status testing see Rubella – Immunity Serology.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

Rubella diagnosis

Whole blood or serum

5.0 ml blood, or 1.0 ml serum

Vacutainer tubes (SST)

Rubella diagnosis

Plasma

1.0 ml

EDTA/Lavender top tube

Submission and Collection Notes

1

Suspected Rubella in Pregnancy: Indicate that the patient is pregnant and request ‘Diagnosis’ on the General Test Requisition Form. Also provide the patient’s symptoms, date of onset, vaccination history or record of prior immunity if known. 

2

Rubella IgG and IgM will be tested when diagnosis is requested on the General Test Requisition Form.

3

Do not submit glass tubes.

Limitations

Hemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing.

Preparation Prior to Transport

Label the specimen container with the patient’s full name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

Special Instructions

Centrifuge if using SST. Place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to PHOL on ice packs ASAP, where possible.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Rubella diagnostic serology (IgG and IgM) is performed daily Monday to Saturday. 

Turnaround time for test results is up to 5 days from receipt by PHO laboratory.

Reporting

Results are reported to the ordering physician or health care provider named on the requisition.

Specimens that are positive (reactive) for Rubella IgM are also reported to the appropriate Medical Officer of Health as per Health Protection and Promotion Act.

Test Methods

The Rubella IgG and IgM tests are performed using ELISA (Enzyme Linked Immunosorbent Assay) test kits manufactured by Euroimmun (Germany). The IgG and IgM ELISA tests are both quantitative (IgG) and semi-quantitative (IgM) measuring human antibodies of the IgG and IgM classes against rubella virus in serum or plasma. Test results are reported qualitatively together with a clinical interpretation based on the status of both IgG and IgM.

Interpretation

After a primary infection, both IgG and IgM antibodies develop within 3-7days after rash onset. Both antibodies then increase reaching a plateau 2-3 weeks later.

Antibody levels may be reported as Non-Reactive (no detectable antibody), Indeterminate (the level of antibody detected is considered borderline reactive or equivocal) or Reactive (antibody is detectable within the positive range of the assay).

Non-Reactive and Indeterminate levels of   both IgG and IgM antibodies may be observed in the acute stage of infection rising to reactive levels in subsequent weeks. 

In the absence of acute infection, indeterminate levels of IgG may represent very low levels of antibody many years after initial infection or vaccination whereas indeterminate levels of IgM may be due to declining levels of IgM several months post infection or possibly due to assay non-specificity.

If the acute blood sample shows low reactive, indeterminate or non reactive IgG and/or IgM results then a convalescent sample should be collected. Recent infection is confirmed if a significant rise in antibody levels is observed between acute and convalescent sera.

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Updated 4 Jan 2019