Measles – Diagnostic Serology

Testing Indications

When Measles infection is suspected - Contact Public Health Ontario 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 measles.

Diagnosis for symptomatic patients or post exposure, requires additional samples for testing by PCR, refer to the test information sheet Measles-Diagnostic PCR for specimen collection and testing information.

Specimen Collection and Handling

Specimen Requirements

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

Measles Diagnosis

Whole blood or serum

5.0 ml whole blood or 1.0 ml serum

Blood, clotted - vacutainer tubes (SST)

Measles Diagnosis

Plasma

1.0 ml

Lavender top tube

Submission and Collection Notes

1

Test performed will be Measles IgG and IgM if date of onset and clinical symptoms are indicated on the General Test Requisition Form.

Timing of Specimen Collection

Acute: Collect the acute sample within 7 days after the onset of the rash.

Convalescent: Collect the convalescent sample 7 to 10 days after the acute.

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

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)

Measles diagnostic serology testing to detect Measles 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 Measles IgM are also reported to the appropriate Medical Officer of Health as per Health Protection and Promotion Act.

Test Methods

The Measles 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 measles 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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Laboratory Services

customerservicecentre@oahpp.ca

Updated 4 Jan 2019