Test Id : WNVS
West Nile Virus, RNA, PCR, Molecular Detection, Serum
Useful For
Suggests clinical disorders or settings where the test may be helpful
Rapid testing for West Nile virus (WNV) RNA (lineage 1 and lineage 2) using serum specimens
An adjunctive test to serology for detection of early WNV infection (ie, first few days after symptom onset)
This test should not be used for screening asymptomatic individuals and should only be used to test patients with signs and symptoms of WNV disease.
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
The following algorithms are available:
-Meningitis/Encephalitis Panel Algorithm
-Mosquito-borne Disease Laboratory Testing
Method Name
A short description of the method used to perform the test
Real-Time Reverse Transcription Polymerase Chain Reaction (RT-PCR)
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
Arbovirus
Flavivirus
Mosquito Borne Encephalitis
Viral encephalitis
West Nile PCR
West Nile Virus (WNV)
WNV PCR
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
The following algorithms are available:
-Meningitis/Encephalitis Panel Algorithm
-Mosquito-borne Disease Laboratory Testing
Specimen Type
Describes the specimen type validated for testing
Serum
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container: Sterile container
Specimen Volume: 0.5 mL
Collection Instructions:
1. Within 2 hours of collection centrifuge and aliquot serum into a sterile container.
2. Serum specimens not aliquoted from the serum gel collection tube into a sterile container will be rejected.
Special Instructions
Library of PDFs including pertinent information and forms related to the test
Forms
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
0.3 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
| Gross hemolysis | Reject |
| Heat-inactivated specimen | Reject |
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 7 days | |
| Frozen | 7 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Rapid testing for West Nile virus (WNV) RNA (lineage 1 and lineage 2) using serum specimens
An adjunctive test to serology for detection of early WNV infection (ie, first few days after symptom onset)
This test should not be used for screening asymptomatic individuals and should only be used to test patients with signs and symptoms of WNV disease.
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
The following algorithms are available:
-Meningitis/Encephalitis Panel Algorithm
-Mosquito-borne Disease Laboratory Testing
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
West Nile virus (WNV) is a mosquito-borne flavivirus (single-stranded RNA virus) that primarily infects birds but occasionally infects horses and humans (1,2,3). Until the virus was recognized in 1999 in infected birds in New York City, WNV had been detected only in the Eastern hemisphere with a wide distribution in Africa, Asia, the Middle East, and Europe. There are 2 distinct lineages of WNV: lineage 1 has the broadest distribution worldwide, including North America and Europe, whereas lineage 2 is found only in Africa and parts of Europe.
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%) results in meningitis or encephalitis. 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 are at particularly high risk.
Laboratory diagnosis is best achieved by demonstration of specific IgG- and IgM-class antibodies in serum specimens. However, polymerase chain reaction (PCR) testing can be used to detect WNV RNA in serum, whole blood, and urine specimens from patients with recent WNV infection (ie, 3-5 days following infection) when specific antibodies to the virus are not yet present. It may also be useful for patients who are immunocompromised when an antibody response is minimal or absent. Finally, PCR can be useful for supporting a serologic diagnosis, given the known cross-reactivity of WNV serology with other flaviviruses.
Studies indicate that whole blood testing by PCR may provide higher sensitivity when testing patients with acute WNV disease (up to 87%) compared to serum, plasma, urine, and cerebrospinal fluid testing.(4) However, viral RNA may be detected for a longer period of time (> or =10 days after symptom onset) in urine than in other sources.(5) Serum testing offers lower sensitivity (26%) but may be used when it is the only specimen type available.
Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative
Reference values apply to all ages.
Interpretation
Provides information to assist in interpretation of the test results
A positive result indicates the presence of West Nile virus RNA and is consistent with early infection.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The sensitivity of the assay is very dependent upon the time of illness onset in which the specimen is collected. Polymerase chain reaction testing has the greatest utility when used within the first few days of symptom onset.
Whole blood rather than serum has been shown to provide increased sensitivity for detecting West Nile virus (WNV) RNA.
A negative test does not exclude infection with WNV. Therefore, the results obtained should be used in conjunction with clinical findings and serologic test results to make an accurate diagnosis.
This assay detects both viable and nonviable virus. Test performance depends on viral load in the specimen and may not correlate with cell culture performed on the same specimen.
Supportive Data
The following validation data supports the use of this assay for clinical testing.
Accuracy/Diagnostic Sensitivity and Specificity:
Accuracy studies were performed by testing negative clinical specimens with whole viral genomic RNA for lineages 1 and 2 near the limit of detection (LOD) and yielded greater than or equal to 97% sensitivity and specificity.
Analytical Sensitivity/LOD:
The lower LOD of this assay is 1 to 5 target copies/mcL of RNA extract for serum, urine, and spinal fluid and 27 to 60 copies/mcL for EDTA whole blood.
Precision:
Inter-assay and intra-assay precisions are 100%.
Specificity:
A panel of 42 organisms that can be found in the specimen types acceptable for this assay, as well as closely-related viruses (eg, dengue types 1-4, Japanese encephalitis virus, hepatitis E virus, Murray Valley encephalitis virus, St. Louis encephalitis virus, tick-borne encephalitis virus, yellow fever virus, Zika virus) and those that can cause a similar clinical syndrome were tested by this assay. No cross-reacting positive results were noted.
Reportable Range:
This is a qualitative assay, and the results are reported as either negative or positive for targeted West Nile virus.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Petersen LR, Brault AC, Nasci RS. West Nile virus: review of the literature. JAMA. 2013;310(3):308-315
2. Colpitts TM, Conway MJ, Montgomery RR, Fikrig E. West Nile virus: Biology, transmission, and human infection. Clin Microbiol Rev. 2012;25(4):635-648
3. Centers for Disease Control and Prevention (CDC), National Center for Emerging and Zoonotic Infectious Disease (NCEZID), Division of Vector-Borne Diseases (DVBD): West Nile Virus. CDC; Accessed January 21, 2025. Available at https://www.cdc.gov/west-nile-virus/
4. Lustig Y, Mannasse B, Koren R, et al. Superiority of West Nile virus RNA detection in whole blood for diagnosis of acute infection. J Clin Microbiol. 2016;54(9):2294-2297
5. Barzon L, Pacenti M, Franchin E, et al. Excretion of West Nile virus in urine during acute Infection. J Infect Dis. 2013;208(7):1086-1092
Method Description
Describes how the test is performed and provides a method-specific reference
This real-time reverse transcription polymerase chain reaction (RT-PCR) assay provides qualitative detection of lineages 1 and 2 of West Nile virus. Viral RNA is first extracted from serum on an automated platform. The extract is then used for subsequent RT-PCR. An initial reverse transcription step is employed to convert viral RNA to complementary DNA (cDNA). The viral cDNA target is then amplified on the Roche LightCycler 480 using specific primers and detected via Taqman probe technology. An internal control is also included with each reaction. Analysis of the PCR amplification is accomplished through the use of LightCycler software.(Package insert: RealStar WNV RT-PCR Kit 2.0. Altona Diagnostics; 03/2020)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Monday through Friday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location
Indicates the location of the laboratory that performs the test
Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
- Authorized users can sign in to Test Prices for detailed fee information.
- Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
- Prospective clients should contact their account representative. For assistance, contact Customer Service.
Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.
CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
87798
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| WNVS | West Nile Virus RNA, PCR, Serum | 32361-8 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 608436 | West Nile Virus RNA, PCR, Serum | 32361-8 |