Test ID: WNVP
West Nile Virus (WNV), Molecular Detection, PCR, Plasma
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Rapid testing for West Nile virus (WNV) RNA
As an adjunct in the diagnosis of early WNV virus infection
Method Name A short description of the method used to perform the test
Real-Time Polymerase Chain Reaction (PCR)/RNA Probe Hybridization
(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Flavivirus
Mosquito Borne Encephalitis
Viral Encephalitis
West Nile PCR
West Nile Virus (WNV)
WNV PCR
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube: Lavender top (EDTA)
Specimen Volume: 0.8 mL
Forms: If not ordering electronically, submit a Microbiology Request Form (Supply T244) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | NA |
| Icterus | NA |
| Other | Plasma gel tube |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Plasma EDTA | Refrigerated (preferred) | 7 days |
| Frozen | 7 days |
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. 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/84186 West Nile Virus [WNV] Antibody, IgG and IgM, Serum or WNVC/88680 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)
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.
Not applicable
Positive results will be reported as WNV nucleic acid detected.
Interpretation Provides information to assist in interpretation of the test results
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)
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This assay should not be used for screening asymptomatic individuals, and should only be used to test patients with signs and symptoms of West Nile virus (WNV) disease.
The sensitivity of the assay is very dependent upon the quality of the specimen submitted.
A negative test does not exclude infection with WNV. Therefore, the results obtained should be used in conjunction with clinical findings 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.
Possible cross-reactivity with other flaviviruses (eg, dengue virus, St. Louis encephalitis virus, and Japanese Encephalitis virus) may occur.
Supportive Data
The following validation data supports the use of this assay for clinical testing.
Accuracy/Diagnostic Sensitivity and Specificity:
To determine the ability of the assay to detect RNA from clinical specimens, 30 negative whole blood, serum, plasma, and CSF samples (120 total) were spiked with West Nile virus positive control material at the limit of detection (approximately 10 targets/microliter). The specimens were run in a blinded manner along with 30 negative (nonspiked) specimens for each matrix. 100% of the specimens were positive and 100% of the nonspiked specimens were negative.
To supplement the above data, blinded proficiency panels were tested with this assay and demonstrated 100% concordance. In addition, 8 patient samples that were positive for West Nile virus RNA by this assay were tested with an alternative reference lab assay. Results showed 75% concordance.
Analytical Sensitivity/Limit of Detection (LoD):
The lower limit of detection (LoD) of this assay is approximately 10 targets/microliter.
Precision:
Inter-assay precision is 100% and intraassay precision is 100%.
Reference Range:
Fifty CSF samples from normal donors were tested and found to be negative for targeted West Nile virus RNA.
Reportable Range:
This is a qualitative assay and the results are reported as either negative or positive for targeted West Nile virus.
Method Description Describes how the test is performed and provides a method-specific reference
This LightCycler PCR assay has been optimized to detect common conserved sequences in the nonstructural protein of West Nile virus (WNV). Viral nucleic acid is extracted by the MagNA Pure automated instrument (Roche Applied Science) from cerebrospinal fluid, or plasma. Primers directed to the nonstructural protein amplifies a specific sequence of the virus. For the test, WNV genomic RNA is transcribed to cDNA. The LightCycler instrument amplifies and monitors the development of target nucleic acid sequences after the annealing step during PCR cycling by fluorescence assay. This automated PCR system utilizes stringent air-controlled temperature cycling and capillary cuvettes to rapidly detect (30-40 minutes) amplicon development. The detection of amplified products is based on the fluorescence resonance energy transfer (FRET) principle. For FRET product detection, a hybridization probe with a donor fluorophore, fluorescein, on the 3'-end is excited by an external light source and emits light that is absorbed by a second hybridization probe with an acceptor fluorophore, LC-Red 640, at the 5'-end. The acceptor fluorophore then emits a light of a different wavelength that can be measured with a signal that is proportional to the amount of specific PCR product. Analysis of the PCR amplification and probe melting curves are accomplished through the use of LightCycler software.(Cockerill FR III, Uhl JR: Applications and challenges of real-time PCR for the clinical microbiology laboratory. In Rapid Cycle Real-Time PCR Methods and Applications. Edited by U Reischel, C Wittwer, F Cockerill. Berlin, Germany, Springer-Verlag; 2002, pp 3-30)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Saturday; Continuously 7 a.m.-8 p.m. (June through November)
Monday, Wednesday, Friday; 6 a.m. (December through May)
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
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 The location of the laboratory that performs the test
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's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
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 Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
87798
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| SRC97 | Specimen Source | 31208-2 |
| 56072 | Result | 34892-0 |
| 56073 | Special Information | 48767-8 |
| 56074 | Report Status | In Process |
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