West Nile virus assay

Test in Focus

Mayo Clinic Laboratories’ updated West Nile virus test is a polymerase light chain assay that enables increased sensitivity to detect the potentially serious, mosquito-borne flavivirus infection. In this Test in Focus episode of the "Answers From the Lab" podcast, Bobbi Pritt, M.D., discusses how the test identifies West Nile virus RNA in whole blood, urine, cerebrospine fluid, and serum; detects virus presence much earlier than traditional approaches; and is able to detect lineages 1 and 2.

“There aren’t a lot of tests out there that are commercially available for both lineages,” Dr. Pritt says. “Now this is really important in a global society. Both lineages can cause potentially serious neuro-invasive disease. You don’t want to miss the viral infection because your test isn’t completely inclusive.”

Increasing testing sensitivity enables differentiation between West Nile and similar vector-borne infections.

“We know that there’s a lot of cross-reactivity between West Nile virus — the antibodies that the host forms to that virus — and other flaviviruses like Zika and Dengue virus, so a positive result doesn’t always mean it’s West Nile,” Dr. Pritt explains. “But then having that PCR result confirm that provides a positive diagnosis,” she says. Listen to learn more about how updated West Nile virus testing provides certainty in detecting the challenging virus.

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Useful for


  • Rapid testing for West Nile virus (WNV) RNA (lineage 1 and lineage 2)
  • An adjunctive test to serology for detection of early WNV infection (i.e., first few days after symptom onset).
  • This assay should not be used for screening asymptomatic individuals and should only be used to test patients with signs and symptoms of WNV disease.

WNVBL | West Nile Virus, RNA, PCR, Molecular Detection, Blood

  • Blood may provide greater sensitivity for PCR detection of WNV RNA than other sources.

WNVUR | West Nile Virus, RNA, PCR, Molecular Detection, Urine

  • The WNV PCR may remain positive for longer in urine than blood, serum and CSF (7 days or more).

Specimen requirements

WNVBL | West Nile Virus, RNA, PCR, Molecular Detection, Blood

  • Container/Tube: Lavender top (EDTA)
  • Specimen Volume: 1 mL

WNVUR | West Nile Virus, RNA, PCR, Molecular Detection, Urine

  • Container/Tube: Sterile container
  • Specimen Volume: 1 mL
  • Collection Instructions:
    • Collect random urine in a sterile container.
    • Label specimen as urine.

WNVS | West Nile Virus, RNA, PCR, Molecular Detection, Serum

  • Collection Container/Tube:
  • Preferred: Serum gel
  • Acceptable: Red top
  • Submission Container: Sterile container
  • Specimen Volume: 0.5 mL
  • Collection Instructions:
    • Centrifuge and aliquot the serum into a sterile container within 6 hours of collection.
    • Label specimen as serum.

WNCSF | West Nile Virus, RNA, PCR, Molecular Detection, Spinal Fluid

  • Container/Tube: Sterile vial
  • Specimen Volume: 0.5 mL
  • Collection Instructions: Do not centrifuge or heat inactivate.

Performance information

  • Analytic Time: 1 day
  • Days Performed: Monday through Friday

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Samantha Rossi

Samantha Rossi is a Digital Marketing Manager at Mayo Clinic Laboratories. She supports marketing strategies for product management and specialty testing. Samantha has worked at Mayo Clinic since 2019.