Type of test Microscopic
Normal findings
IgM ≤ 0.9 ISR (immune status ratio)
IgG
Vaccinated: positive (≥ 1.1 AI [antibody index])
Unvaccinated: negative (≤ 0.8 AI)
Culture: no growth
Test explanation and related physiology
Varicella is an acute infectious disease caused by varicella zoster virus (VZV). The recurrent infection, herpes zoster, is also known as shingles. VZV is a DNA virus and is a member of the herpesvirus group that includes herpes simplex types 1 and 2; see p. 501). Like other herpesviruses, VZV has the capacity to persist in the body after the primary (first) infection as a recurrent and latent infection. VZV persists in sensory nerve ganglia. Primary infection with VZV results in chickenpox. The recurrent or latent infections cause herpes zoster (shingles).
Testing for VZV or the antibodies produced in response to VZV is not routinely used to diagnose active cases of chicken pox and shingles, which are detected by the person’s signs and symptoms. It may be performed in pregnant women, newborns, in people before organ transplantation, and in those with HIV/ AIDS. Testing may also be used to determine if someone has been previously exposed to VZV either through past infection or vaccination and has developed immunity to the disease. It can distinguish between an active or prior infection. It can determine whether someone with severe or atypical symptoms has an active VZV infection or has another condition with similar symptoms.
Recovery from primary varicella infection usually results in lifetime immunity. Herpes zoster, or shingles, occurs when latent VZV reactivates and causes recurrent disease. Postherpetic neuralgia (pain in the area of the zoster) may persist after the zoster has resolved. This can be reduced by aggressive and early antiviral treatment.
Testing is also recommended to confirm varicella outbreaks or establish varicella as a cause of death. A variety of serologic tests for varicella antibody are available commercially and can be used to assess disease-induced immunity. The most frequent source of VZV isolation is vesicular fluid. Serum is used for serologic testing and some molecular assays.
Live-attenuated varicella virus is now part of the measles mumps–rubella and varicella vaccine (e.g., ProQuad) for use in children. A herpes zoster vaccine is available for persons 50 years of age and older to minimize the risk of herpes zoster.
Procedure and patient care
Before
* Explain the procedure to the patient.
*Tell the patient that no preparation is required.
During
• Specimens are best collected by unroofing a vesicle, preferably a fresh fluid-filled vesicle, and then rubbing the base of a skin lesion with a polyester swab.
• For serologic testing, collect whole venous peripheral blood in serum separator (gold, marble or grey) vacutainer.
• For the blood spot method:
- Prick the subject’s finger using a lancet.
- Collect a sufficient quantity of blood onto both defined areas on the filter strip so that the spot expands to the circular border. Permit the specimen to air dry completely.
After
• Check for bleeding.
Abnormal findings
-Acute varicella infection
-Herpes (varicella) zoster
- Varicella immunity
