West Nile Virus Antibodies, IgM by ELISA, Serum

Abbrev Code:WNM   
Order Code:LAB6474Order Name:West Nile Virus IGM
Methodology:Enzyme-linked immunosorbent assay
CPT Codes: 86788 x1
Turnaround Time:Specimens are sent to the reference laboratory Mon-Sat; results are reported within 2-7 days.
Special Instructions:Parallel testing is preferred. Label samples as acute or convalescent.

Collection Instructions

Optimal Volume:2 mL
Minimum\Peds Volume:0.5 mL
Container:Red or gold (gel)
Alternate Containers: Red (no gel)
Causes for Rejection:Plasma, hemolyzed, severely lipemic, heat inactivated.

Processing and Shipping

Specimen Processing:Separate serum from cells within 2 hours of collection. Centrifuge and aliquot 1 mL, 0.15 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Stability:After separation from cells: 48 hours at room temperature; 2 weeks refrigerated; 1 year frozen.
Test Performed at or Referral Lab Lab Sendouts  (ARUP)
Referral Lab number:50236


Reference Range:

1.11 or greater

IgM positive. An index value of >1.10 indicates IgM antibodies to West Nile virus were detected. The presence of IgM antibodies is presumptive evidence that the patient was or is infected with (or exposed to) West Nile virus. A patient can be IgM positive, but not currently infected with West Nile virus because of 1) cross-reactivity to other flaviviruses, rheumatoid factor or enteroviruses, or 2) IgM antibodies to previous infections may be present for over 500 days. Because other members of the Flaviviridae family, such as St. Louis encephalitis show extensive cross-reactivity with West Nile virus, serologic testing specific for these species should also be performed. Results should be used in correlation to clinical history or other data.


IgM equivocal. Index values in this range are considered an equivocal result. It is recommended that samples with equivocal results be redrawn two or more weeks later and retested with this assay.

0.89 or less

IgM negative. An index value of <0.90 indicates IgM antibodies to West Nile virus were not detected. The absence of IgM antibodies is presumptive evidence that the patient was not infected with West Nile or another flavivirus. However, the sample may have been drawn before antibodies were detectable, or the patient may be immunosuppressed. If infection is suspected, another sample should be drawn 7-14 days later and retested.



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