VZV infection causes two clinically distinct forms of disease. Primary infection with VZV results in varicella (chickenpox), characterized by vesicular lesions in different stages of development on the face, trunk, and extremities. Herpes zoster, also known as "shingles, " � results from reactivation of endogenous latent VZV infection within the sensory ganglia. This clinical form of the disease is characterized by a painful, unilateral vesicular eruption, which usually occurs in a restricted dermatomal distribution. The diagnosis of these two diseases is usually made clinically. However, the use of diagnostic assays may be important in specific situations.
Other names include chickenpox serology testing.
Use
To assist in the diagnosis of acute-phase infection with varicella virus
To assist in identifying nonimmune individuals
Interpretation
Normal range: Negative.
A positive IgG result coupled with a positive IgM result indicates recent infection with VZV.
A positive IgG result coupled with a negative IgM result indicates previous exposure to VZV and immunity.
A negative IgG result coupled with a negative IgM result indicates the absence of prior exposure to VZV and no immunity. However, a negative result does not rule out a VZV infection. Negative results in suspected early VZV infections should be followed by testing a new serum specimen in 2 " �3 weeks.
Equivocal results should be followed up with testing a new serum specimen within 10 " �14 days.
Limitations
Test for VZV IgG antibodies is of use when clinical symptoms are present or infection suspected. Screening of the general population leads to no appreciable diagnostic advantage. Results from immunosuppressed patients should be interpreted with caution.
Many different antibody tests are available with a wide range of performance standards. The fluorescent antibody to membrane antibody (FAMA) is the most extensively validated assay and correlates best with susceptibility to and protection against varicella. However, this test is not widely used because it is labor intensive and requires expert interpretation.
Many commercially available ELISAs are available that are considered generally less sensitive than FAMA, although specificities are comparable.
Commercial ELISA assays are suitable for screening for VZV susceptibility among health care workers. The rationale for this is that the risk of vaccinating an adult with a false-negative test result is much lower than the risk of natural infection in an individual falsely identified as seropositive.
Routine screening for varicella in individuals born in the United States before 1980, who are not health care workers, is not recommended because of extremely high rates of seropositivity in this population.