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Test ID: WNVP West Nile Virus (WNV), Molecular Detection, PCR, Plasma

Reporting Name

West Nile Virus PCR, P

Useful For

Rapid testing for West Nile virus (WNV) RNA


As an adjunct in the diagnosis of early WNV virus infection

Clinical Information

West Nile virus (WNV) is a mosquito-borne flavivirus (single stranded RNA virus) that primarily infects birds, but occasionally infects horses and humans. Until the virus infection was recognized in 1999 in birds in New York City, WNV was found only in the Eastern hemisphere, with a wide distribution in Africa, Asia, the Middle East, and Europe.(1-3) Most people who are infected with WNV do not experience symptoms. It is estimated that about 20% of those who become infected will develop West Nile fever with mild symptoms including headache, myalgia, and occasionally a skin rash on the trunk of the body. About 1 of 150 WNV infections (<1%) result in meningitis or encephalitis. Case fatality rates among patients hospitalized during recent outbreaks have ranged from 4% to 14%. Advanced age is the most important risk factor for death, and patients older than 70 years of age are at particularly high risk.


Laboratory diagnosis is best achieved by demonstration of specific IgG and IgM class antibodies in serum or cerebrospinal fluid (CSF) specimens (WNV / West Nile Virus [WNV] Antibody, IgG and IgM, Serum or WNVC / West Nile Virus [WNV] Antibody, IgG and IgM, Spinal Fluid).


The specific identification of WNV by detection of IgM in CSF is the recommended test to document central nervous system disease, but this test may be falsely negative in CSF collected <8 days after the onset of symptoms. Alternatively, experiences in nucleic acid testing for WNV RNA in blood prior to transfusion have indicated that PCR can detect viremic target RNA from patients with known West Nile infection when specific antibodies to the virus are not present (ie, from 2-8 days after onset of symptoms).(4,5)


The likelihood of detection of West Nile virus RNA by PCR is relatively low. In cerebrospinal fluid, the clinical sensitivity is approximately 55%, and in blood, about 10%. Specificity of the assay in either matrix is approximately 100%.(6)

Testing Algorithm

See Mosquito-borne Disease Laboratory Testing in Special Instructions.

Analytic Time

Monday through Thursday: 2 days Friday, Saturday: 3 days

Day(s) and Time(s) Performed

Monday through Saturday; Continuously 7 a.m.-8 p.m. (June through November)

Monday, Wednesday, Friday; 6 a.m. (December through May)

Clinical Reference

1. Brinton MA: The molecular biology of West Nile Virus: a new invader of the western hemisphere. Ann Rev Microbiol. 2002;56:371-402

2. Petersen LR, Marfin AA: West Nile virus: a primer for the clinician. Ann Intern Med. 2002;137(3):173-179

3. Petersen LR, Roehrig JT: West Nile virus: a reemerging global pathogen. Emerg Infect Dis. 2001;7(4):611-614

4. Busch MP, Tobler LH, Saldanha J, et al: Analytical and clinical sensitivity of West Nile virus RNA screening and supplemental assays available in 2003. Transfusion. 2005;5(4):492-499

5. Epstein JS: Insights on donor screening for West Nile virus. Transfusion. 2005;45(4):460-462

6. New York City Department of Health. West Nile surveillance and control: an update for healthcare providers in New York City. City Health Information. June 2001;20(2)

Method Name

Real-Time Polymerase Chain Reaction (PCR)/RNA Probe Hybridization

Specimen Type

Plasma EDTA

Specimen Required

Collection Container/Tube: Lavender top (EDTA)

Submission Container/Tube: Screw-capped, sterile container

Specimen Volume: 1 mL

Collection Instructions: Spin down promptly

Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma EDTA Refrigerated (preferred) 7 days
  Frozen  7 days

Reference Values


Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
WNVP West Nile Virus PCR, P 34892-0


Result ID Test Result Name Result LOINC Value
56072 West Nile Virus PCR, P 34892-0


If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-CNS-Infections, mml-Pediatric