Varicella – Serology
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This page provides serological testing information for Varicella at Public Health Ontario (PHO). For information regarding other testing options, refer to the following PHO web pages:
Testing Indications
Serology for Varicella Zoster (IgG) may be indicated to determine immune status following a natural infection or post-vaccination and assess infants suspected of having congenital varicella syndrome.
Unknown Immunization Status: Immunization vs. Serology
If a patient’s immunization records are unavailable, immunization with a Varicella-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 immunization documentation or serologic proof of immunity regardless of their birth year.
When Varicella Zoster (Chicken Pox/Shingles) infection is suspected – contact your local public health unit (PHU) before collecting specimens. Refer to the 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 Varicella-Zoster Virus Detection test information sheet, for specimen collection and testing information.
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Varicella Immunity |
Whole blood or serum |
5.0 ml whole blood or 1.0 ml serum |
Blood, clotted – serum separator tube (SST) |
|
Varicella Diagnosis |
Whole blood or serum |
5.0 ml whole blood or 1.0 ml serum |
Blood, clotted – serum separator tube (SST) |
Submission and Collection Notes
Complete all fields of the requisition form, including:
- Test(s) requests and indications for testing
- Patient setting
- Specimen type and source
- Outbreak or investigation number
- Clinical information (acute/recent infection, vaccination history, relevant signs, symptoms, and/or clinical history, and onset date).
Label the specimen container(s) with the patient’s first and last name, collection date, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens and Serology Testing – Laboratory Specimen Collection and Submission Instructions. Failure to provide this information may result in rejection or testing delay.
Varicella IgG testing will be performed on all requests for Varicella immunity serology.
Varicella IgG and IgM testing will only be performed on diagnostic requests when clinical information is provided on the General Test Requisition Form.
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 specimen is preferred to improve the chances of observing a change in the antibody levels.
Limitations
Hemolysed, icteric, lipemic or microbially 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.
All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.
Test Frequency and Turnaround Time (TAT)
Varicella serology to detect Varicella IgG and IgM is performed daily Monday to Friday.
Turnaround time is up to 5 days from receipt at PHO’s laboratory.
STAT and Critical Specimens Testing
STAT testing is not available.
Priority testing is available for the diagnosis of varicella in symptomatic patients or persons exposed to a confirmed case. Requests for priority testing must be reviewed and approved by a PHO Medical Microbiologist in conjunction with the appropriate Public Health practitioner. Priority specimens must be packaged separately from routine specimens using TDG-compliant packaging and labelling. To assist with laboratory workflow and identifying 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 Varicella IgG and IgM tests are performed using chemiluminescence immunoassay technology to qualitatively determine specific IgG and IgM antibodies to the Varicella virus in human serum.
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.
The following table provides possible test results with associated interpretations:
| IgG | IgM | Interpretation |
|---|---|---|
| Non Reactive | Not Tested | No evidence of immunity (Indicates susceptibility). |
| Reactive | Not Tested | Evidence of past infection/vaccination; Evidence of immunity. |
| Not Tested | Non Reactive | No serological evidence of recent or acute Varicella-Zoster infection. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Not Tested | Indeterminate | Varicella-Zoster IgM antibody status inconclusive. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Not Tested | Reactive | May indicate recent or acute Varicella-Zoster infection. Does not rule out assay non-specificity. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Non Reactive | Non Reactive | No serological evidence of recent or past Varicella-Zoster infection. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Non Reactive | Indeterminate | Varicella-Zoster IgM antibody status inconclusive. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Non Reactive | Reactive | May indicate recent or acute Varicella-Zoster infection. Does not rule out assay non-specificity. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Reactive | Non Reactive | Suggests no recent primary infection; Evidence of past exposure. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Reactive | Indeterminate | Varicella-Zoster IgM antibody status inconclusive. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
| Reactive | Reactive | May indicate recent or acute Varicella-Zoster infection. Does not rule out assay non-specificity. If clinically indicated, please submit a new sample to monitor for any significant change in antibody level. |
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.
Varicella IgG test results are reported qualitatively together with an interpretation of the patient’s immune status based on the level of Varicella IgG detected.
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