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Test Code WNVBL West Nile Virus, RNA, PCR, Molecular Detection, Blood


Specimen Required


Container/Tube: Lavender top (EDTA)

Specimen Volume: 1 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send whole blood specimen in original tube. Do not aliquot.


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 (ie, first few days after symptom onset), with blood specimens potentially providing a greater sensitivity than other sources for WNV RNA detection

 

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.

Method Name

Real-Time Reverse Transcription Polymerase Chain Reaction (RT-PCR)

Reporting Name

West Nile Virus RNA, PCR, Blood

Specimen Type

Whole Blood EDTA

Specimen Minimum Volume

See Specimen Required

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Refrigerated 7 days

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

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.(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 (≥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

Negative

Reference values apply to all ages.

Interpretation

A positive result indicates the presence of West Nile virus RNA and is consistent with early infection.

Day(s) Performed

Monday through Friday

Report Available

Same day/1 to 5 days

Specimen Retention Time

1 week

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

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

87798

LOINC Code Information

Test ID Test Order Name Order LOINC Value
WNVBL West Nile Virus RNA, PCR, Blood 34460-6

 

Result ID Test Result Name Result LOINC Value
608438 West Nile Virus RNA, PCR, Blood 34460-6

Forms

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