Chickenpox and Shingles Tests
At a Glance
Why Get Tested?
If your doctor suspects that you have, or have recently had, chickenpox or shingles and a diagnosis is necessary; to show immunity to the varicella zoster virus (VZV) or the potential for re-activating a VZV infection before receiving immunosuppressive drugs
When to Get Tested?
To check immune status and/or to find an active infection; sometimes when a person has unusual (atypical) and/or severe symptoms and the doctor wants to distinguish between a VZV infection and another cause; prior to an organ transplant or when pregnant woman, or an immune-compromised person has been exposed to someone with chickenpox
Sample Required?
A blood sample is taken from a vein in your arm for VZV antibody testing; to detect the virus itself, a sample of fluid from a blister (vesicle), blood, cerebrospinal fluid, or other body fluid or tissue
Test Preparation Needed?
No test preparation is needed.
The Test Sample
What is being tested?
Tests for chicken pox and shingles are done to find and diagnose either a current or past infection with the virus (varicella zoster virus (VZV)) that causes these conditions. Most often, testing is not necessary because a diagnosis of active infection can be made by the doctor just from clinical signs and symptoms, but in some patients with an atypical skin disease, 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 lung fluids and saliva. 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 occurs, followed by the a pimple-like papules that become small, fluid-filled blisters (vesicles). The blisters break, form a crust, and then heal. This process occurs in two or three waves or “crops” of several hundred blisters over a few days.
Once the first infection has got better, the virus becomes hidden (latent) in sensory nerve cells. The person develops antibodies during the infection that usually prevent them from getting chickenpox again if infected by the virus. However, later in life and in those with immune systems that are not working properly, VZV can reactivate, moving 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 several places. Several days after the pain, itching, or tingling begins, a rash, with or without blisters, forms in the same place. In most people, the rash and pain reduces within a few weeks, and the virus again becomes hidden (latent). A few may have pain that lingers for several months.
Most cases of chickenpox and shingles get better 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 growing 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 growing 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 patient. Antibody testing requires a blood sample collected 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.
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.
The Test
How is it used?
Active cases of chickenpox and shingles, which are caused by the varicella zoster virus (VZV), are usually diagnosed just on the person’s symptoms and clinical presentation. Most adults have been infected with VZV, therefore, general population screening is not done. However, testing for VZV or for the antibodies produced in response to VZV infection may be done in certain cases. For example, it may sometimes be done in pregnant women, in newborns, in patients prior to organ transplantation, and in those with HIV/AIDS. The reasons for testing may include:
- to determine if someone has been previously exposed to VZV either through past infection or vaccination and has developed immunity to the disease
- to distinguish between an active or prior infection
- to determine whether someone with severe or unusual (atypical) symptoms has an active VZV infection or has another condition with similar symptoms
There are several methods of testing for VZV:
Antibody testing
When you are exposed to VZV, your immune system responds by producing antibodies to the virus. Two types of VZV antibodies may be found in the blood: IgM and IgG. IgM antibodies are the first to be produced by the body in response to a VZV infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and declines. Eventually, the level (titre) of VZV IgM antibody usually falls below detectable levels. Additional IgM may be produced when the hidden (latent) VZV is reactivated. IgG antibodies are produced by the body several weeks after the initial VZV infection to provide long-term protection. Levels of IgG rise during the active infection, then stabilize as the VZV infection resolves and the virus becomes inactive. Once a person has been exposed to VZV, they will have some measurable amount of VZV IgG antibody in their blood for the rest of their life. VZV IgG antibody testing can be used, along with IgM testing, to help confirm the presence of a recent or previous VZV infection.
Viral detection
Viral detection involves finding VZV in a blood, fluid, or tissue sample. This can be done either by growing (culturing) the virus or by detecting the virus’s genetic material (VZV DNA).
- VZV culture is now rarely performed — a sample of fluid is collected from a blister (vesicle) (the most common sample). It is incubated in a culture of live cells and nutrients to grow and isolate the virus. This test is sensitive and specific, but it takes 2 or more days to complete. Fresh lesions are the best for this test. Viral shedding decreases over time and can lead to a false negative result.
- VZV DNA testing – performed to detect VZV genetic material in a patient sample. This method is sensitive. It can identify and measure the amount of the virus.
- Direct Fluorescent Antibody (DFA) – this test visualizes the presence of VZV in the cells taken from the patient’s skin lesion using a special microscope and labelled antibody. It is rapid, but less specific and sensitive than the VZV culture and DNA testing.
The choice of tests and samples collected depends on the patient, their symptoms, and on the doctor’s clinical findings.
When is it requested?
VZV antibody tests may be requested to check immune status and/or to identify a recent infection. VZV culture or DNA tests may be requested when a newborn or immune-compromised person has been exposed to VZV and is ill with unusual (atypical) and/or severe symptoms – to detect an active primary VZV infection in the baby or a primary or reactivated infection in the immune-compromised person.
What does the test result mean?
Care must be taken when interpreting the results of VZV testing. The doctor evaluates the results in conjunction with clinical findings. It can sometimes be difficult to distinguish between a latent and active VZV infection. This is possible for several reasons, including:
- A healthy person who has been infected with VZV will continue to have the the virus hidden after the symptoms have disappeared. The VZV can reactivate intermittently, often sub-clinically, shedding small amounts of virus into body fluids but not causing symptoms.
- An infant or immune-compromised person may not have a strong antibody response to the VZV infection – their IgM and IgG levels may be lower than expected even though they have an active case of VZV.
- The virus may not be present in sufficient number in the particular fluid or tissue tested to be detected.
Antibody detection
If both VZV IgG and IgM are present in a person who has symptoms, then it is likely that they have either been recently exposed to VZV for the first time and has chickenpox or that the previous VZV infection has been reactivated and they has shingles.
If only IgM is present, then the infection may have been very recent. If a newborn has IgM antibodies, then they have a congenital VZV infection. If a person is symptomatic but has low or undetectable levels of IgG and/or IgM, it may mean that they either has a disease other than VZV or that his immune system is not working normally and not producing a measurable level of VZV antibody.
Viral detection
If someone is symptomatic and the culture is positive for varicella zoster virus, then the person is likely to have an active VZV infection. If the culture is negative, then the person’s symptoms may be due to another cause or the VZV virus is not detectable in the sample tested.
If a test for VZV DNA is positive, then VZV is present. High levels of viral DNA tend to indicate an active infection. Low levels indicate a VZV infection but may not indicate a symptomatic condition. Negative results do not rule out VZV infection – the virus may be present in very low numbers or may not be present in the body sample tested.
Is there anything else I should know?
There is now a vaccine available for older adults that is intended to decrease the risk for having a re-activation of the virus that presents as shingles and decreases the severity of the disease if it does occur. It is not yet in widespread use and its ultimate effect on the incidence of shingles remains to be seen.
VZV may rarely cause encephalitis, a serious complication.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
