Measles – Serology

Testing Indications

Serology for Measles Immunity (Measles IgG) may be indicated to determine immune status either following natural infection or post-vaccination.

Unknown Immunization Status: Immunization vs. Serology
If a patient’s immunization records are unavailable, immunization with Measles-containing vaccine is preferred, rather than ordering serology to determine immune status. This avoids the potential for false positive results, reduces the risk of missed opportunities for immunization and is consistent with advice from the Canadian Immunization Guide (CIG). This does not apply to specific occupational groups, such as healthcare workers, who require either documentation of immunization or serologic proof of immunity regardless of their birth year.

When Measles infection is suspected – contact your local public health unit (PHU) prior to collecting specimens. Refer to STAT and Critical Specimens Testing section for instructions on sending priority specimens to PHO’s laboratory.

Diagnosis of symptomatic patients requires additional samples for testing by PCR. Refer to the Measles-Diagnostic PCR test information sheet, for specimen collection and testing information.

Subacute sclerosing panencephalitis (SSPE), is a rare neurological disorder of children and young adults related to a persistent Measles viral infection. Neurological symptoms present several years after the initial infection with progressive deterioration. SSPE testing is indicated for patients exhibiting neurological symptoms with a history of Measles infection at an early age.

Acceptance/Rejection Criteria

• Laboratory results for total IgG and total albumin are mandatory and must be provided on both PHO General Test Requisition and National Microbiology Laboratory (NML) requisition.
• Both CSF and blood (serum or plasma) specimens must be submitted.

Failure to meet these criteria will result in sample cancellation. It is recommended to contact PHO’s customer service at 416-235-6556 or 1-877-604-4567 prior to collection to co-ordinate advanced notice to NML to order reagents and for support on specimen requirements.

Timing of Specimen Collection

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

Convalescent Specimen: Collect the convalescent sample a minimum of 7 and up to 30 days after the acute sample collection. Collection after 10 days from the acute is preferred to improve the chances of observing a change in the antibody levels.

SSPE specimen: CSF AND serum or plasma should be collected within 1 hour of each other.

Limitations

Hemolysis, icteric, Lipemic or microbial contaminated serum is not recommended for testing.

Storage and Transport

Specimens should be stored at 2-8°C following collection and shipped to PHO’s laboratory on ice packs. Centrifuge if using serum separator tubes (SST). Place the specimen in a biohazard bag and seal.

For SSPE requests, store specimens at 2-8°C if sent to PHO’s laboratory within 6 days of collection. Otherwise, freeze (-20°C or below) and ship frozen on dry ice.

All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Test Frequency and Turnaround Time (TAT)

Measles serology to detect Measles IgG and IgM is performed daily Monday to Saturday. Turnaround time is up to 5 days from receipt at PHO’s Laboratory.

Testing of CSF and blood for suspected SSPE is performed at NML in Winnipeg. The TAT for SSPE is within 21 days from receipt at PHO.

Stat and Critical Specimens Testing

STAT testing is not available.

Priority testing is available for measles diagnosis of symptomatic patients or persons who have been exposed to a confirmed case. Priority specimens must be packaged separate from routine specimen using TDG compliant packaging and labelling. To assist with laboratory workflow and identifiying priority specimens, mark STAT on the outside of the package. Contact customer service at 416-235-6556 or 1-877-604-4567 prior to specimen transfer to provide PHO’s laboratory with the expected arrival time.

The Measles IgG test is performed using the BioPlex 2200 MMRV IgG kit for use with the Bio-Rad Bioplex 2200 System. It is a Multiplex Flow Immunoassay test intended for the qualitative detection of IgG antibodies against Measles in human serum.

The Measles IgM test is performed using chemiluminescence immunoassay (CLIA) technology for the qualitative determination of specific IgM antibodies to Measles virus in human serum. The test is performed on Diasorin’s Liaison® XL Analyzer platform.

Specimens submitted for SSPE are tested at NML for anti-Measles IgG antibodies in the CSF and serum using the Euroimmun kit. The ratio of Measles specific antibodies in comparison to the ratio of total IgG or total albumin in the CSF and the serum (CSQrel) is used to determine whether there is an indication of Measles-specific antibody production in the central nervous system (CNS).

Interpretation

Following a primary infection, both IgG and IgM antibodies develop within 3-7 days 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 - level of antibody detected is considered borderline reactive or equivocal
• 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 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 (greater than 2-fold) in antibody levels is observed between acute and convalescent sera.

For interpretation guidelines of SSPE testing please refer to NML’s Guide to Test for SSPE.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Measles IgG test results are reported qualitatively together with an interpretation of the patient’s immune status based on the level of Measles IgG detected.

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