West Nile Virus

Specimen Collection and Handling

Specimen Requirements

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

West Nile Virus Serology

Blood or serum

5.0 ml blood or 1.0 ml serum

Vacutainer tubes (SST) 

West Nile Virus Serology


400 µl

Sterile container

West Nile Virus PCR

EDTA blood, plasma (or serum)2

5.0 ml blood or 1.0 ml plasma or serum

Non-heparin anticoagulant/Lavender top tube

Submission and Collection Notes


If submitting CSF, you must also submit a serum sample


CSF Serology is the preferred method of testing


Molecular testing must must be preapproved by the PHO laboratory microbiologist. Contact PHO laboratory Customer Service at 416-235-6556 or 1877-604-4567 to request approval.


Complete the following on the General Test Requisition Form:

  • relevant travel history
  • onset date 
  • symptoms

Instructions for using SST tubes are found in the document titled: LAB-SD-008, Blood Collection using Serum Separator Tubes


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

Preparation Prior to Transport

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

Specimens for molecular testing should be frozen and shipped on dry ice.

Special Instructions

Instructions for using SST tubes are found in the document titled: LAB-SD-008, Blood Collection Using Serum Separator Tubes.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

West Nile virus IgG and IgM ELISA testing is performed daily Monday to Friday during peak season (summer months) and up to twice per week at other times.

TAT for non-reactive ELISA IgG and IgM is up to 2 days during peak season and up to 5 days at other times.

TAT for a confirmed reactive ELISA IgM is 2 to 5 days.

TAT for results on samples tested by PRNT is up to 10 days.


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

Specimens that are positive for West Nile virus are reported to the Medical Officer of Health as per the Health Protection and Promotion Act.

Test Methods

Specimens for West Nile virus-(WNV) IgG and IgM serology are performed using enzyme–linked immunosorbent assay (ELISA).

Note: As of May 17, 2021, two changes were made to the WNV testing algorithm:

1. The indeterminate range for the Euroimmun IgM assay was increased from a ratio of 0.8 to 1.1 to a ratio of 0.8 to 2.0.

2. A second confirmatory assay, Focus Diagnostics WNV IgM EIA blanking test, was added to confirm West Nile IgM positive results when Euroimmun IgM results are reactive (ratio >2.0).
Specimens may also undergo plaque reduction neutralization testing (PRNT).

West Nile avidity testing may be considered in order to differentiate recent (last few months) from remote infections. This should only be considered in patients with severe illness (e.g. hospitalized). Contact PHOL Customer Service to speak to a microbiologist for approval.

For further testing information refer to labstract titled: LAB-SD-011, West Nile Virus Update - Interpretation of serology results and investigation of cases with neurological involvement.

Data and Analysis

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Contact Laboratory Customer Service

Laboratory Services


Updated 31 May 2021