Varicella Zoster Virus AB (IgG) Test · Blood

If you have ever had chickenpox or received the varicella vaccine, your immune system should have built lasting protection against the virus that causes both chickenpox and shingles. But "should have" is not the same as "did." This test answers a simple, high-stakes question: are you actually immune, or could you still get seriously sick from a virus most people assume they are protected against?

The answer matters more than you might expect. Chickenpox in an unprotected adult can cause severe pneumonia, liver damage, and dangerous blood clotting problems. Shingles, the painful reactivation of the same virus later in life, can cause lasting nerve pain and, in rare cases, stroke or vision loss. Knowing your immunity status is especially urgent if you are pregnant, about to start immune-suppressing medication, or planning an organ transplant.

What This Test Measures

VZV IgG (varicella zoster virus immunoglobulin G) is a specific antibody protein produced by your B cells, a type of white blood cell, after your body encounters the varicella zoster virus through natural infection or vaccination. Once produced, this antibody typically persists for life, serving as a biological record of past exposure and a front line of defense against re-infection.

The test measures the concentration of this antibody in your blood. A positive result means your immune system has encountered VZV before and mounted a response. A negative result means you lack detectable antibodies and may be susceptible to primary varicella (chickenpox). An equivocal result falls in a gray zone and usually warrants retesting or vaccination.

Who Is Most at Risk Without Immunity

In most adults, VZV IgG is positive. A study of 1,184 pregnant women in Norway found 98.6% were VZV IgG positive. A Slovenian population study of 3,689 people found roughly 86% had detectable antibodies across all ages, with near-universal positivity in adults. The small percentage of adults who test negative are at genuine risk if exposed.

Certain groups are more likely to lack immunity. Adults who grew up in tropical climates, where chickenpox circulates less in childhood, may never have been exposed. People on medications that suppress B cells (the cells that make antibodies) can lose previously established immunity over time. In a study of rheumatoid arthritis patients on conventional or biologic medications, VZV IgG levels were significantly lower than in matched healthy controls, suggesting that chronic inflammatory disease and its treatments can erode VZV protection.

Vaccine Response and Antibody Durability

If you were vaccinated as a child, the two-dose varicella series produces strong initial antibody responses. In a Japanese study of 37 children, 100% were VZV IgG positive after the second dose. But antibody levels decline over time. By the time those same children were entering elementary school (about 4 to 5 years later), the proportion still showing protective antibody levels had dropped to 43 to 59% depending on the assay used.

This does not necessarily mean those children lost all protection. Immune memory extends beyond what antibody levels alone can show, because T cells (another branch of the immune system) also contribute to defense. But declining antibody levels are the reason some vaccinated individuals still develop breakthrough chickenpox, and why this test can reveal a gap you would not otherwise know about.

For older adults, the recombinant shingles vaccine (Shingrix) boosts VZV-specific antibodies substantially. In a study of 68 adults comparing dialysis patients to healthy controls, the vaccine produced roughly a five-fold rise in VZV IgG in dialysis patients and a nine-fold rise in controls within two weeks of the second dose. Even a year later, levels remained above baseline in both groups.

Immunity in Immunocompromised People

If you are taking medications that suppress your immune system, your VZV IgG result requires extra attention. Solid organ transplant recipients, for instance, may have lower antibody quality, measured as "avidity" or how tightly the antibody grips its target, even when their total VZV IgG concentration appears normal. A study of 90 kidney and liver transplant recipients found reduced VZV-specific cellular responses alongside lower antibody avidity compared to healthy controls.

B cell-depleting therapies like rituximab (used in autoimmune diseases and some cancers) can gradually erode your existing antibody levels. In a study of 15 patients with a neurological autoimmune condition treated with rituximab for a median of 70 months, total IgG declined by about 0.42 g/L per year, and several pathogen-specific antibodies dropped alongside it.

If you are about to start one of these medications, checking your VZV IgG beforehand gives your doctor a chance to vaccinate you while your immune system can still mount a response. Once deep immunosuppression is established, live vaccines are usually off the table.

Connection to Shingles and Neurological Risk

Having VZV IgG does not guarantee you will never get shingles. The virus remains dormant in your nerve cells for life, and shingles occurs when your cellular immunity (T cells, not antibodies) weakens enough to let the virus reactivate. A large Japanese study of over 12,500 adults found that VZV-specific T cell immunity, not antibody levels, was the factor that correlated with shingles risk and severity.

Large population studies have linked clinical shingles episodes to a modest increase in later dementia risk. A Korean study of over 752,000 adults found that VZV infection was associated with about a 41% higher risk of dementia over roughly a decade of follow-up (adjusted for age, sex, and other conditions). An Italian study of nearly 133,000 people found a 13% higher dementia risk after severe, hospitalized shingles over up to 23 years. These studies used clinical shingles diagnoses, not IgG titers, so the VZV IgG test itself does not predict dementia risk directly. But they reinforce why maintaining strong VZV immunity through vaccination matters.

Assay Sensitivity Varies

Not all VZV IgG tests are equally reliable, and this is worth knowing if your result comes back negative or equivocal. A study of 176 children with inflammatory bowel disease compared a standard commercial VZV IgG assay to a more sensitive research-grade test that targets a specific viral protein. The standard assay detected immunity in only 69% of children, while the more sensitive test found 90% were actually immune.

This means a negative result on a standard commercial assay does not always mean you lack immunity, particularly if you have a documented history of chickenpox or two vaccine doses. If your result is negative and you have a clear exposure history, discuss with your doctor whether retesting with a more sensitive method or simply revaccinating makes more sense.

Reference Ranges

VZV IgG results are reported differently depending on the lab and assay used. There are no universal "optimal" ranges for this test. Instead, results fall into three categories defined by each manufacturer's cutpoints. The following are representative thresholds, but your lab's specific values may differ slightly.

These cutpoints come from assay manufacturers and vary between labs. One commonly used research threshold defines seronegative as 200 mIU/mL or below on a WHO-calibrated test. Compare your results within the same lab over time rather than across different labs or assay platforms.

When Results Can Be Misleading

The biggest source of misleading results is assay sensitivity, not timing or lifestyle factors. Unlike hormones or metabolic markers, VZV IgG is not affected by fasting, time of day, recent meals, or a single bout of exercise. It is a stable marker of immune memory, not a rapidly fluctuating measurement.

• Assay type: Standard commercial assays can miss true immunity in up to 20 to 30% of vaccinated or previously infected individuals, as shown in studies of children with inflammatory bowel disease. A negative result on a less sensitive test does not always mean you are unprotected.
• Immunosuppressive medications: B cell-depleting drugs (rituximab, ocrelizumab), fingolimod, and other potent immune therapies can lower VZV IgG over months to years. A previously positive result may become negative during treatment, reflecting genuine erosion of immunity rather than a lab artifact.
• Timing after vaccination: If tested too soon after a first vaccine dose (within two to three weeks), antibodies may not yet be detectable. Wait at least four weeks after vaccination before testing.
• Infants under 12 months: Babies carry their mother's VZV antibodies, which decline with a half-life of roughly 25 days. A positive result in a newborn reflects maternal immunity, not the baby's own immune response.

Tracking Your Trend

For most healthy adults, VZV IgG is a one-time test. If your result is clearly positive and you are not on immunosuppressive therapy, you can be confident in your immunity without serial monitoring.

The exception is if you are immunocompromised or on medications that suppress B cell function. In that case, periodic retesting (annually or after changes in therapy) can detect waning immunity before it leaves you vulnerable. If you receive the shingles vaccine, retesting four to six weeks after the second dose can confirm your immune system responded. If you are on rituximab or a similar drug long-term, yearly VZV IgG alongside total immunoglobulin levels can help you and your doctor decide whether additional protective measures (antiviral prophylaxis or revaccination during a treatment break) are needed.

What to Do With Your Result

If your result is positive and you are otherwise healthy, no further action is needed for varicella immunity specifically. If you are over 50, consider the recombinant shingles vaccine regardless of your IgG level, because shingles prevention depends more on T cell immunity than on antibody levels alone.

If your result is negative or equivocal, the next step depends on your situation. For healthy, non-pregnant adults, the standard recommendation is a two-dose varicella vaccine series. For pregnant women, vaccination must wait until after delivery. For people about to start immunosuppressive therapy, vaccinating before treatment begins is the priority, ideally at least four weeks beforehand to allow time for an immune response.

If your result is negative but you have a clear history of chickenpox or two documented vaccine doses, the assay may be undersensitive. Discuss retesting with a more sensitive glycoprotein-based test or simply proceeding with vaccination, which is safe even if you already have some underlying immunity.