Varicella – Serology

Testing Indications

Serology for Varicella (VZV) may be indicated for diagnosis of acute/recent varicella infection, to determine immune status (either following natural infection or post-vaccination), and for the assessment of infants suspected of having congenital varicella syndrome.

Varicella- Zoster (Chicken Pox) in Pregnancy: Please ensure that a suspect case of Chicken Pox or Shingles in a pregnant woman is clearly marked for Varicella-Zoster Diagnosis and that both VZV IGG and IGM serology are ordered. 

For all diagnostic requests submit samples of vesicle scrapings or fluid for virus detection according to the instructions in the test information sheet for Varicella Zoster Virus – Culture.

Specimen Collection and Handling

Specimen Requirements

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

VZV IgG and/or VZV IgM

Whole blood or serum

5.0 ml whole blood or 1.0 ml serum

Blood, clotted – vacutainer tubes (SST)

VZV IgG and/or VZV IgM

Plasma

5.0 ml

EDTA Lavender top tube

Submission and Collection Notes

1

VZV IgG testing will be performed on all requests for VZV serology

2

VZV IgG and IgM testing will only be performed when the following clinical information is provided on the General Test Requisition Form indicating acute/recent infection, relevant signs, symptoms, and/or clinical history, and onset date.

Limitations

Haemolyzed, 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 PHO laboratory on ice packs ASAP, where possible.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Varicella IgG and IgM serology is performed daily Monday to Friday.

Turnaround time 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 for Varicella IgM are to be reported to the Medical Officer of Health as per Health Protection and Promotion Act.

Test Methods

The Varicella-Zoster 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 Varicella-zoster 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.

Please Note: The antibody response following viral reactivation (Shingles) may differ from that following acute infection with chicken pox. VZV IgM may not be detected post viral reactivation however in cases where viral reactivation occurs many decades after primary chicken pox, IgM may once again be produced. Elevated levels of VZV IgG are also often seen post virus reactivation.

For more information concerning the interpretation of diagnostic IgM and IgG serology refer to the document titled: LAB-SD-044, Diagnostic Interpretation of Viral Specific IgM and IgG Serology.

Mis à jour le 21 mai 2019