Chickenpox and Shingles Tests

Tests for chicken pox and shingles are performed to detect and diagnose either a current or past infection with the virus that causes these conditions, the varicella zoster virus (VZV). Most often, testing is not necessary because a diagnosis of active infection can be made from clinical signs and symptoms, but in some patients with atypical skin lesions, a diagnostic test helps to confirm the infection. In organ transplant recipients or pregnant women, the tests may be useful to diagnose a current infection or to determine status of immunity.

Varicella zoster is a member of the herpes virus family. It is very common and the primary infection is highly contagious, passing from person to person through respiratory secretions. VZV causes chickenpox in the young and in adults who have not been previously exposed. Usually, about two weeks after exposure to the virus, an itchy rash emerges, followed by the formation of pimple-like papules that become small, fluid-filled blisters (vesicles). The vesicles break, form a crust, and then heal. This process occurs in two or three waves or “crops” of several hundred vesicles over a few days.

Once the initial infection has resolved, the virus becomes latent, persisting in sensory nerve cells. The person develops antibodies during the infection that usually prevent them from getting chickenpox again during subsequent exposures. However, later in life and in those with compromised immune systems, VZV can reactivate, migrating down the nerve cells to the skin and causing shingles (also known as herpes zoster). Symptoms of shingles include a mild to intense burning or itching pain in a band of skin at the waist, the face, or another location. It is usually in one place on one side of the body but can also occur in multiple locations. Several days after the pain, itching, or tingling begins, a rash, with or without vesicles, forms in the same location. In most people, the rash and pain subside within a few weeks, and the virus again becomes latent. A few may have pain that lingers for several months.

Most cases of chickenpox and shingles resolve without complications. In people with compromised immune systems, such as those with HIV/AIDS or those who have had an organ transplant, it can be more severe and long-lasting. In some cases, it may not become latent and may spread to the central nervous system.

In pregnant women, the effects of exposure to VZV on a fetus or newborn depend on when it occurs and on whether or not the mother has been previously exposed. In the first 20 to 30 weeks of pregnancy, a primary VZV infection may, rarely, cause congenital abnormalities in the fetus. If the infection occurs one to three weeks before delivery, the baby may be born with or acquire chickenpox after birth, although the baby may be partially protected by the mother’s antibodies. If a newborn is exposed to VZV at birth and does not have maternal antibody protection, then the VZV infection can be fatal.

Until the introduction and widespread use of a varicella zoster vaccine in 1995, nearly everyone in the United States became infected by VZV by the time they were an adult. While VZV is still present in its latent form in most adults, according to the Centers for Disease Control and Prevention, the incidence of new cases of chickenpox in children has declined by about 90%.

The sample required depends on whether testing is being done to determine the presence of antibodies or to detect the virus itself and on the health status of the patient. Antibody testing requires a blood sample drawn from a vein in the arm. Viral detection may be done on a variety of samples, including a sample of vesicle fluid, blood, cerebrospinal fluid, other fluid, or tissue.

No test preparation is needed.