Have you ever wondered what happens when your doctor suspects you have chicken pox? Maybe you’ve got those telltale itchy spots, or perhaps you were exposed to someone with the virus. Whatever the reason understanding how medical professionals test for chicken pox can help ease your mind during an already uncomfortable situation.
As someone who’s researched viral testing extensively I’m excited to share everything you need to know about chicken pox testing. Let’s dive right in!
What Is Chicken Pox Anyway?
Before we talk about testing let’s quickly review what we’re dealing with. Chicken pox (varicella) is caused by the varicella-zoster virus (VZV) which is a type of herpes virus. This same virus can reactivate later in life to cause shingles (herpes zoster).
The virus is super contagious and causes that infamous itchy, blistering rash along with fever, headache, and fatigue. While many doctors can diagnose chicken pox just by looking at the rash, laboratory testing is sometimes necessary for confirmation.
When Is Testing for Chicken Pox Necessary?
Not everyone with suspected chicken pox needs testing. Doctors often recommend testing in these situations:
- To confirm suspected cases of chicken pox
- To verify chicken pox as the cause of outbreaks
- To confirm diagnosis in severe cases (hospitalizations or deaths)
- To investigate unusual presentations
- To determine if someone is immune to chicken pox
- To check if adverse events after vaccination were caused by the vaccine strain
Testing is especially important for people at higher risk of complications, including:
- Pregnant women
- Infants
- Teens and adults with chicken pox symptoms
- People with weakened immune systems due to:
- HIV, cancer, or other conditions
- Organ transplants
- Medications like chemotherapy or steroids
The Main Types of Chicken Pox Tests
When it comes to testing for chicken pox, doctors have several options. Here are the main tests they might use:
1. PCR Test (Polymerase Chain Reaction)
What it is: PCR testing looks for genetic material (DNA) from the varicella-zoster virus in a sample.
How it’s done: A healthcare provider gently swabs an open blister to collect fluid or takes a small scab sample.
Why it’s preferred: PCR is the gold standard for confirming chicken pox because it’s:
- Fast (results often available within a day)
- Extremely sensitive and specific
- Able to detect even small amounts of virus
As the CDC puts it, “PCR is the most helpful laboratory test for confirming cases of varicella and herpes zoster.”
2. Viral Culture Test
What it is: Cells from a swab sample are grown in a lab to check for VZV.
How it’s done: Similar to PCR, a swab from a blister is collected.
Limitations:
- Not as accurate as PCR
- Takes longer to get results
- Less commonly used today
3. Direct Fluorescent Antibody (DFA) Test
What it is: This test uses a fluorescent dye and special microscope to look for VZV in a sample.
How it’s done: Also requires a swab from a blister.
Advantages/Disadvantages:
- Provides rapid results
- Not as accurate as PCR
- Still used in some clinical settings
4. Antibody Blood Tests
What they are: Blood tests that look for VZV antibodies (proteins your immune system makes to fight the virus).
How they’re done: A healthcare professional takes a blood sample from a vein in your arm.
Types of antibody tests:
- IgM antibody test – Shows current or recent VZV infection
- IgG antibody test – Shows if you’ve ever been exposed to VZV (through infection or vaccination)
Antibody tests are particularly useful when:
- No blisters are available to sample
- Checking for immunity to chicken pox
- Determining if someone needs vaccination
The Testing Process: What to Expect
If your doctor recommends testing for chicken pox, here’s what typically happens:
For Blister/Lesion Tests (PCR, Viral Culture, or DFA)
- Your healthcare provider will identify a suitable blister or scab
- They’ll gently press a cotton swab on the blister to collect fluid
- The sample is sealed and sent to a laboratory
- Results usually come back within a few days (PCR can be as quick as one day)
The whole collection process takes less than five minutes and causes minimal discomfort.
For Blood Tests (Antibody Testing)
- A healthcare professional will clean an area on your arm
- They’ll insert a small needle into a vein to draw blood
- The blood sample is collected in a tube
- You might feel a brief sting when the needle goes in and out
- The sample is sent to a lab for analysis
- Results usually take a few days
No special preparation is needed for either type of test.
What Do the Test Results Mean?
Understanding your test results is important:
If You Have Symptoms and Test Positive for VZV
This confirms you have either chicken pox or shingles. Your doctor will determine which one based on:
- Your age
- The pattern and appearance of the rash
- Your specific symptoms
If You Don’t Have Symptoms but Test Positive
This means you either:
- Had chicken pox in the past
- Received the chicken pox vaccine
- Are currently fighting off the virus without showing symptoms
If You Test Negative
If your symptoms strongly suggest chicken pox but your test is negative, your doctor might:
- Order a different type of test
- Consider other conditions with similar symptoms
- Diagnose based on clinical presentation despite negative results
Specialized Testing Situations
In some cases, more advanced testing may be performed:
Virus Strain Identification
PCR testing can distinguish between wild-type VZV and the vaccine strain. This is important for:
- Investigating vaccine-related adverse events
- Confirming if a vaccinated person got chicken pox from the vaccine or natural exposure
- Research purposes
Testing for Immunity (IgG Avidity)
Some specialized labs can perform tests that determine not just if you have antibodies, but how strongly they bind to the virus. This helps distinguish between:
- Recent infection (low avidity antibodies)
- Past infection (high avidity antibodies)
This isn’t commonly done in regular clinical settings but can be helpful in research or complex cases.
Where is Chicken Pox Testing Available?
Testing for chicken pox is available through:
- Hospital laboratories
- Commercial reference laboratories
- Public health laboratories
- The CDC Herpesvirus Laboratory (for special cases)
Your doctor will determine the appropriate testing facility based on your situation.
Prevention is Better Than Testing
The best way to avoid needing a chicken pox test is to prevent infection in the first place!
Chicken Pox Vaccine Recommendations
The CDC recommends the chicken pox vaccine for:
Children:
- First dose at 12-15 months
- Second dose at 4-6 years
People 13 years and older who never had chicken pox:
- Two doses, at least 28 days apart
Shingles Vaccine (Shingrix)
For those who’ve already had chicken pox, the CDC recommends:
- Shingrix vaccine for healthy adults 50 and older
- Also recommended for adults 19+ with weakened immune systems
- Two doses, separated by 2-6 months
Even if you’ve had shingles before, you should still get vaccinated since you can get shingles more than once.
My Experience with Chicken Pox Testing
I remember when my nephew broke out in spots that looked suspiciously like chicken pox. Despite being vaccinated, breakthrough cases can happen. His pediatrician took a small sample from one of his blisters for PCR testing, and we had confirmation within 24 hours.
The testing process was quick and relatively painless for him. It gave us peace of mind knowing exactly what we were dealing with, which helped us take appropriate precautions to prevent spreading it to vulnerable family members.
Final Thoughts
While most chicken pox cases can be diagnosed by a healthcare provider just by looking at the characteristic rash, laboratory testing provides valuable confirmation in uncertain or high-risk situations.
PCR testing of blister fluid or scabs remains the most reliable method, but antibody testing also plays an important role, especially when checking for immunity or when lesions aren’t available for sampling.
If you suspect you or your child has chicken pox, don’t hesitate to contact your healthcare provider. They’ll determine if testing is necessary and guide you through the process.
Have you or your child ever been tested for chicken pox? What was your experience like? I’d love to hear about it in the comments!
Remember: This article is for informational purposes only and shouldn’t replace professional medical advice. Always consult with a healthcare provider if you suspect chicken pox or have questions about testing.
Polymerase chain reaction (PCR)
PCR is the most useful laboratory test for confirming suspected varicella and herpes zoster. PCR can detect VZV DNA rapidly and sensitively in skin lesions (vesicles, scabs, maculopapular lesions).
- Vesicular lesions or scabs, if present, are the best for sampling.
- Adequate collection of specimens from maculopapular lesions in vaccinated people can be a challenge.
- However, one study1 that compares a variety of specimens from the same patients vaccinated with one dose suggests that maculopapular lesions collected with proper technique are a highly reliable specimen types for the detection of VZV.
- Other sources, such as nasopharyngeal secretions, saliva, urine, bronchial washings, and cerebrospinal fluid are less likely to provide an adequate sample; they often lead to false negative results.
DFA tests, viral culture, and Tzanck smears
Other viral isolation techniques for the confirmation of varicella are direct fluorescent antibody assay (DFA) and viral culture. However, these techniques are generally not recommended because they are less sensitive than PCR. In the case of viral culture, these techniques take longer to generate results.
Like DFA, a Tzanck smear has a rapid turnaround time but is not recommended because of its limited sensitivity and is not specific for VZV. Moreover, real-time PCR protocols can be completed within one day.
Serologic methods have limited use for laboratory confirmation of herpes zoster and should only be used when suitable specimens for PCR testing are not available.
IgM serologic testing is considerably less sensitive than PCR testing of skin lesions. IgM serology provides evidence for a recent active VZV infection. However, it cannot distinguish between primary infection and reinfection or reactivation from latency. This is because specific IgM antibodies are produced with each exposure to VZV. IgM tests are also inherently prone to poor specificity.
Measuring acute and convalescent sera also has limited value, since it is difficult to detect an increase in IgG for laboratory diagnosis of herpes zoster.
Paired acute and convalescent sera showing a four-fold rise in IgG antibodies have excellent specificity for varicella. However, they are not as sensitive as PCR of skin lesions for the diagnosis of varicella. People with a prior history of vaccination or disease may have very high baseline titers and may not achieve a four-fold increase in the convalescent sera. The usefulness of this method for diagnosing varicella is further limited as it requires two office visits. A single positive IgG ELISA result cannot confirm a varicella case.
- The preferred diagnosis method is a demonstration of VZV DNA by PCR tests from a clinical specimen, ideally scabs, vesicular fluid, or cells from the base of a lesion.
- PCR is also useful for confirming breakthrough varicella. Other methods, such as DFA and culture, are available for diagnosis but are less sensitive and specific than PCR.
- Positive serologic test for varicella-zoster immunoglobulin M (IgM) antibody when a varicella-like rash is present.
- Four-fold or greater rise in serum varicella immunoglobulin G (IgG) antibody titer by any standard serologic assay between acute and convalescent sera.
For both unvaccinated and vaccinated people, PCR is the most reliable method for confirming a VZV infection.
Learn about guidelines for collecting and shipping specimens for VZV testing (varicella and herpes zoster). These include methods for VZV serologic assays and VZV PCR/genotyping, sources for suitable supplies, and how to submit specimen to CDC.
PCR testing and genotyping can distinguish between wild-type VZV and vaccine-type (Oka/Merck) strains of VZV.
Such testing is used in situations when it is important to recognize the two VZV strains, like in suspected vaccine adverse events. Examples of possible varicella vaccine-adverse events include:
- Varicella or a varicella-related complication in a vaccinated person 7 to 42 days after vaccination.
- Herpes zoster in a vaccinated person.
- Suspected secondary vaccine-strain VZV transmission.
Samples of blood, cerebrospinal fluid, biopsy, or autopsy specimens may also be tested for vaccine-strain/wild-type VZV discrimination to confirm etiology and to identify a vaccine-adverse event. However, these specimens and can lead to false negative results.
The CDC Herpesvirus Laboratory and APHL Vaccine Preventable Diseases Reference Centers can distinguish wild-type VZV from Oka strain using both strain differential real-time PCR and PCR combined with restriction fragment length polymorphism. Each center (WI, CA, NY, MN) receives specimens from designated states.
A single serologic IgG test can determine if a person has antibodies to VZV from past varicella disease or who may be candidates for varicella-zoster immune globulin (VZIG). The product available in the United States is VariZIG.
Commercial enzyme-linked immunosorbent assays (ELISAs) are the recommendation for screening. Whole infected cell (wc) ELISA is the most commonly used test to determine if a person has antibodies to VZV from past varicella disease. Wc ELISA taken from blood samples can readily detect seroconversion to natural infection with VZV.
Routine testing for varicella immunity following vaccination is unnecessary because commercially available VZV IgG assays are not sensitive enough to detect all seroconversions after a vaccination.
The more sensitive purified glycoprotein ELISA (gpELISA) has been used in research settings to detect seroconversion after vaccination. However, testing with gpELISA is not available commercially.
IgG avidity in research settings determines if a person who is IgG positive for VZV was infected with the virus in the past or more recently.
The laboratory at CDC developed an IgG avidity assay, which determines if the most recent VZV rash was due to primary infection (varicella) or reactivation (herpes zoster).
- High avidity is an indicator of a remote infection.
- Low avidity is an indicator of VZV primary infection.
People infected in the past tend to have antibodies with a high affinity for binding to the antigen. People with a more recent infection tend to have a low affinity.
Vaccinated people undergo antibody affinity maturation following vaccination, which leads to moderate to high IgG avidity VZV antibody. Measurements of VZV avidity in vaccinated people are unlikely to distinguish remote infection (or vaccination) from recent (breakthrough) infection with VZV. This test is not available commercially.
Doctor explains CHICKENPOX | Causes, Stages, Symptoms, Treatment (PLUS PHOTOS)
FAQ
How do doctors confirm chickenpox?
Most often, health care providers find out you have chickenpox based on the rash. Chickenpox also can be confirmed with lab tests, including blood tests or a tissue study of samples of affected skin.
How do they test if you have had chicken pox?
What happens during chickenpox and shingles testing? You will need to provide a sample of blood from your vein or from the fluid in one of your blisters. Blood tests check for antibodies to the VZV. Blister tests check for the virus itself.