West Nile Virus Antibody IgG
West NIle Virus Antibody IgM
Monday through Friday(June through October)
Monday, Wednesday, Friday(November through May)
IgG: NegativeIgM: Negative
Reference values apply to all ages.
IgM: Presence of specific IgM class antibodies in a serum specimen is consistent with acute-phase infection with West Nile virus. By the eighth day of illness, most infected persons will have detectable serum IgM antibody to WNV; in most cases it will be detectable for at least 1 to 2 months after onset of illness, in some cases it will be detetable for 12 months or longer. Absence of the IgM class antibodies to WNV is consistent with lack of acute-phase infection with this virus. Specimens drawn too early in the acute phase (eg, before 8 days postinfection) may be negative for IgM-specific antibodies to WNV. If WNV infection is suspected, a second specimen drawn approximately 14 days postinfection should be tested.
IgG: Presence of specific IgG class antibodies in a serum specimen indicates infection with WNV sometime in the past. By 3 weeks postinfection, virtually all infected persons should have developed IgG antibodies to WNV. If acute-phase infection is suspected, serum specimens drawn within approximately 7 days postinfection should be compared with a specimen drawn approximately 14 to 21 days after infection to demonstrate rising IgG antibody levels between the 2 serum specimens.
In the very early stages of acute WNV infection, IgM may be detectable in CSF before it becomes detectable in serum.