Lab Test

West Nile Antibody, IgM

Vital Encephalitis , ARUP #50236, EPIC: LAB6981, SOFT: XARIM


  • Paired testing is now mandatory for Antibody testing. Please refer to the associated Laboratory Bulletin for more information.
  • Convalescent specimens should be collected 14-21 days after the acute sample but no more than 30 days from the receipt of the acute samples. Please mark sample plainly as "acute" or "convalescent."

Specimen Collection Criteria

Collect (preferred specimen): One Gold-top SST tube.
Also acceptable: One plain Red-top tube.

Physician Office/Drawsite Specimen Preparation

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells within two hours of collection. Transfer serum to a plastic transport tube and refrigerate (2-8°C or 36-46°F).

Preparation for Courier Transport

Transport: 1.0 mL serum, refrigerated (2-8°C or 36-46°F). (Min: 0.15 mL)

Rejection Criteria

  • Hemolyzed specimens.
  • Severely lipemic specimens.
  • Specimens not collected and processed as indicated.


Sunday, Tuesday, Friday.
Results available in 2-6 days.

Reference Range

By report.

Test Methodology

Semi-Quantitative Enzyme-Linked Immunosorbent Assay.

Clinical Utility

This assay is used in the determination of recent infection by demonstration of four-fold increase in IgM antibody level between an acute and convalescent sera. Human infection by these viruses induces an immune response and specific antibody production against the viral antigens. Since viral isolation attempts from these cases are seldom productive, the majority of human cases are diagnosed by serologic means. Seroconversion or an increase in titer between acute and convalescent sera drawn at least 14 days apart of at least four-fold is presumptive evidence of recent infection.

Clinical Disease

Most people infected with West Nile virus have no symptoms of illness, but some may become ill 3 to 15 days after the bite of an infected mosquito. Studies have shown that about 1 in 4 infected persons will have mild illness with fever, headache and body aches, sometimes with skin rash and swollen lymph glands. More severe infection (encephalitis) is less common and may be marked by headache, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. In a few cases, mostly among the elderly, death may occur. Persons with severe or unusual headaches should seek medical care as soon as possible.


  1. Craven, R. Togaviruses In Belshe, R. Textbook of Human Virology, Second Edition, 1991;665 (Eastern Equine Encephalitis)
  2. Craven, R. Flaviviruses In Belshe, R. Textbook of Human Virology, Second Edition, 1991;636. (St. Louis Encephalitis)
  3. Michigan Department of Agriculture, General Information on West Nile Virus, (West Nile Virus)  

CPT Code


Test Codes


Last Updated


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This directory currently reflects information only for specimens collected and/or processed at the
Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.