Back to Test Compendium

West Nile Virus Serology (IgM), Serum - RRPL

Discipline

Microbiology

Overview

Description

  • West Nile Virus (WNV) is transmitted to humans by the Culex species of mosquitos in Canada
  • Most WNV infections are asymptomatic. Some may have mild symptoms including fever, headache, body aches, a mild rash, and/or swollen lymph nodes. In rare cases, WNV can cause encephalitis or meningitis

Ordering Recommendations

  • Symptomatic patients

Specimen Information

Specimen types accepted

  • Serum

Specimen collection container

  • Serum separator tubes (SST; Tiger top or Gold top)

Collection procedure

  • Collect blood in serum separator tube (SST). Serum must be separated from whole blood by centrifugation within 24h of collection.

Required volume

  • 1 SST (tiger or gold Top) tube, 2 mL minimum

Transport and stability

  • Serum must be separated from whole blood within 24h of collection. Serum may be shipped at ambient temperature.

Testing Information

Relevant clinical history

  • WNV IgM results must be interpreted in conjunction with patient symptoms and exposure as WNV IgM antibodies may persist for a year or more.

Clinical interpretation

  • This should be the initial test for diagnosis of suspect West Nile Virus

Performance

Methodology

  • Qualitative IgM immunoassay from Focus Diagnostics (Negative, Indeterminate, or Positive)

Days/times performed

  • All specimens will be tested at RRPL
  • Indeterminate or Positive specimens will be forwarded to the National Microbiology Laboratory (NML) for further testing.

Maximum laboratory time

  • Turnaround time of 3 days from receipt at RRPL
  • Further testing at the NML may take up to 4 weeks

Specimen retention time

  • Serum is retained for 10 days after completion of testing

Other information

  • All Indeterminate or Positive specimens are forwarded to the National Microbiology Lab (NML) for further testing
  • Positive results are reported to a Medical Health Officer

Last Updated: July 28, 2025