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The Test Sample
What is being tested?
Chickenpox and shingles are caused by an infection with the varicella zoster virus (VZV), a member of the herpes virus family. Varicella zoster virus tests detect either antibodies produced by the immune system in response to a VZV infection or detect the virus itself.
Tests for chickenpox and shingles may be performed to detect and diagnose a current or past infection with VZV. Most often, testing is not necessary to diagnosis an active infection because it can be made from clinical signs and symptoms, but in some people with atypical skin lesions, a diagnostic test helps to confirm the infection. In some people, especially organ transplant recipients and pregnant women, the tests may be used to diagnose a current infection or to determine whether or not they have developed immunity from prior infection or by vaccination.
Before the introduction and widespread use of a chickenpox vaccine in 1995, nearly everyone in the United States became infected by VZV by adulthood. While VZV is present in its latent form in many adults who were infected as children, according to the Centers for Disease Control and Prevention, the incidence of new cases of chickenpox has declined significantly. Two doses of the vaccine are about 98% effective in preventing the infection, and those who do become infected usually have milder symptoms.
Varicella zoster virus can cause chickenpox in the young and in adults who have not been vaccinated or previously exposed. The primary infection is highly contagious, passing from person to person through coughing or sneezing or touching fluid from blisters. In a primary infection, signs and symptoms include an itchy rash that emerges about two weeks after exposure to the virus, 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. Photo source: CDC
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. However, later in life and in those with weakened immune systems, the virus can reactivate, migrating down the nerve cells to the skin, 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.
A shingles vaccine is now available for older adults. This vaccine lowers the risk of the virus reactivating as shingles and lessens the severity of the symptoms if shingles do occur. In 2006, the Advisory Committee on Immunization Practices (ACIP) began recommending a shingles vaccination for all adults aged 60 years and older. However, the vaccine is not recommended for those who have weakened immune systems.
Most cases of chickenpox and shingles resolve without complications. In people with weakened immune systems, such as those with HIV/AIDS or organ transplant recipients, the disease 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 developing baby 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 unborn baby. 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.
How is the sample collected for testing?
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 person. 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 body fluid, or tissue.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.