ARUP's Laboratory Test Directory

West Nile Virus Antibody, IgM by ELISA, Serum : 0050236

Mnemonic: WNILE IGM

Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay
Performed: Tue, Fri
Reported: 1-8 days
Specimen Required: Collect: Serum separator tube.

Specimen Preparation: Separate serum from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP Standard Transport Tube. (Min: 0.15 mL) Parallel testing is preferred and convalescent specimens must be received within 30 days from receipt of the acute specimens. Mark specimens plainly as "acute" or "convalescent."

Storage/Transport Temperature: Refrigerated.

Unacceptable Conditions: Plasma. Contaminated, hemolyzed, heat-inactivated, or severely lipemic specimens.

Stability (collection to initiation of testing): After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 year (avoid repeated freeze/thaw cycles)
Reference Interval:
0.89 IV or less: Negative - No significant level of West Nile virus IgM antibody detected.
0.90-1.10 IV: Equivocal - Questionable presence of West Nile virus IgM antibody detected.  Repeat testing in 10-14 days may be helpful.
1.11 IV or greater: Positive - Presence of IgM antibody to West Nile virus detected, suggestive of current or recent infection. 
Interpretive Data: This test is intended to be used as a semi-quantitative means of detecting West Nile virus-specific IgM in serum specimens in which there is a clinical suspicion of West Nile virus infection.  This test should not be used solely for quantitative purposes, nor should the results be used without correlation to clinical history or other data.  Because other members of the Flaviviridae family, such as St. Louis encephalitis virus, show extensive cross-reactivity with West Nile virus, serologic testing specific for these species should be considered.

Seroconversion between acute and convalescent sera is considered strong evidence of current or recent infection. The best evidence for infection is a significant change on two appropriately timed specimens, where both tests are done in the same laboratory at the same time.
CPT Code(s): 86788
Cross References: Arbovirus (West Nile Virus Antibody, IgM by ELISA, Serum), Flavivirus (West Nile Virus Antibody, IgM by ELISA, Serum), Mosquito borne encephalitis (West Nile Virus Antibody, IgM by ELISA, Serum), Viral encephalitis (West Nile Virus Antibody, IgM by ELISA, Serum)