Sign in →

Test ID WNC West Nile Virus Antibody, IgG and IgM, Spinal Fluid

Useful For

Aids in diagnosis of central nervous system infection with West Nile virus

Highlights

In patients with suspected mosquito-borne meningitis or encephalitis, this test detects the presence of IgM and IgG-class antibodies to West Nile virus (WNV) in spinal fluid.

 

This test should be used for diagnostic purposes only.

Profile Information

Test ID Reporting Name Available Separately Always Performed
WNGC West Nile Virus Ab, IgG, CSF No Yes
WNMC West Nile Virus Ab, IgM, CSF No Yes
WNVCI West Nile CSF Interpretation No Yes

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)

Reporting Name

West Nile Virus Ab, IgG and IgM,CSF

Specimen Type

CSF


Specimen Required


Supplies: Aliquot Tube, 5 mL (T465)

Collection Container/Tube: Sterile vial

Submission Container/Tube: Plastic, 5-mL aliquot tube (T465)

Specimen Volume: 1 mL


Specimen Minimum Volume

0.8 mL

Specimen Stability Information

Specimen Type Temperature Time
CSF Refrigerated (preferred) 7 days
  Frozen  30 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

NA

Icterus

NA

Other

NA

Clinical Information

West Nile virus (WNV) is a mosquito-borne flavivirus (single-stranded RNA) that primarily infects birds but can also infect humans and horses. WNV was first isolated in 1937 from an infected person in the West Nile district of Uganda. Until the viral infection was recognized in 1999 in birds in New York City, WNV was found only in the Eastern Hemisphere, with wide distribution in Africa, Asia, the Middle East, and Europe.(1-3) Most recently, in 2012, a total of 5,674 cases of WNV were reported to the CDC, among which 2,873 (51%) were classified as neuroinvasive disease (eg, meningitis or encephalitis) and 286 (5%) cases resulted in death.(2)

 

Most people who are infected with WNV will not develop clinical signs of illness. It is estimated that about 20% of those who become infected will develop West Nile fever with mild symptoms, including fever, headache, myalgia, and occasionally a skin rash on the trunk of the body. 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.(1)

 

Laboratory diagnosis is best achieved by demonstration of specific IgG and IgM class antibodies in serum specimens. PCR (LCWNV / West Nile Virus, Molecular Detection, PCR, Spinal Fluid) can detect WNV RNA in specimens from patients with recent WNV infection (ie, 3-5 days following infection) when specific antibodies to the virus are not yet present. However, the likelihood of detection is relatively low as the sensitivity of PCR detection is approximately 55% in cerebrospinal fluid and approximately 10% in blood, from patients with known WNV infection.

Reference Values

IgG: Negative

IgM: Negative

Reference values apply to all ages.

Interpretation

IgM:

A positive result is consistent with the acute phase of West Nile virus (WNV) meningitis or encephalitis. In the very early stages of acute WNV infection, IgM may be detectable in cerebrospinal fluid (CSF) before it becomes detectable in serum.

 

A negative result may indicate absence of disease. However, specimens drawn too early in the acute phase may be negative for IgM-class antibodies to WNV. If WNV central nervous system infection is suspected, a second specimen should be collected in 1 to 2 weeks and tested.

 

IgG:

A positive result may indicate recent or past central nervous system (CNS) infection with WNV. Clinical correlation is necessary.

 

This assay is unable to distinguish between intrathecal antibody synthesis and serum antibodies introduced into the CSF at the time of lumbar puncture or from a breakdown in the blood-brain barrier. Positive results should be interpreted with other laboratory and clinical data prior to a diagnosis of CNS infection.

Cautions

Test results should be used in conjunction with clinical evaluation, exposure history, and other available diagnostic procedures.

 

The significance of negative test results in immunosuppressed patients is uncertain.

 

False-negative results due to competition by high levels of IgG, while theoretically possible, have not been observed.

 

False-positive results may occur in patients infected with other flaviviruses, including dengue virus, St. Louis virus, and Zika virus and in persons previously infected with West Nile virus (WNV).

 

Because closely related arboviruses exhibit serologic cross-reactivity, it sometimes may be epidemiologically important to attempt to pinpoint the infecting virus by conducting plaque reduction neutralization tests (PRNT) using an appropriate battery of closely related viruses. Such testing is available through the CDC and select public health laboratories.

 

WNV antibody results for cerebrospinal fluid (CSF) should be interpreted with caution. Complicating factors include low antibody levels found in CSF, passive transfer of antibody from blood, and contamination via a traumatic lumbar puncture.

Clinical Reference

1. Petersen LR, Marafin AA: West Nile Virus: a primer for the clinician. Ann Intern Med 2002;137:173-179

2. MMWR: West Nile Virus and Other Arboviral Diseases-United States, 2012. 2013;62(25):513-517

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

4. Centers for Disease Control and Prevention (CDC). Provisional Surveillance Summary of the West Nile Virus epidemic. United States, January-November 2002. MMWR Morb Mortal Wkly Rep 2002;51(50):1129-1133

5. Centers for Disease Control and Prevention (CDC). Investigations of West Nile Virus infections in recipients of blood transfusions. MMWR Morb Mortal Wkly Rep 2002;51(43):973-974

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; 9 a.m.

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

IgG: 86789

IgM: 86788

LOINC Code Information

Test ID Test Order Name Order LOINC Value
WNC West Nile Virus Ab, IgG and IgM,CSF In Process

 

Result ID Test Result Name Result LOINC Value
WNGC West Nile Virus Ab, IgG, CSF 41236-1
WNMC West Nile Virus Ab, IgM, CSF 29569-1
WNVCI West Nile CSF Interpretation 69048-7

NY State Approved

Yes

Secondary ID

36772

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were 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.

Forms

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

Testing Algorithm

The following algorithms are available in Special Instructions:

-Meningitis/Encephalitis Panel Algorithm

-Mosquito-borne Disease Laboratory Testing