The Varicella Zoster Virus (VZV) IgG test is a common screening tool used to determine a person’s immune status against VZV, the virus responsible for causing both chickenpox and shingles. This blood test specifically looks for IgG antibodies, proteins the immune system produces in response to the virus. Identifying the presence or absence of this antibody helps healthcare providers assess whether an individual is protected from future infection. The results are crucial for managing health risks in vulnerable populations where VZV infection could lead to severe complications.
Understanding Varicella Zoster Virus
VZV belongs to the herpesvirus family (human herpesvirus 3) and is highly contagious. Primary infection causes varicella, or chickenpox, which typically presents with an itchy, blistering rash. Following this initial illness, the virus establishes a dormant, or latent, state. The virus travels from the skin to the nervous system, settling within the sensory nerve ganglia. VZV can reside there for decades without causing symptoms. The virus can reactivate later in life, often triggered by a decline in immunity. This reawakening causes herpes zoster, or shingles, a painful, localized blistering rash that follows the path of a single nerve.
What the IgG Antibody Represents
The immune system defends against pathogens like VZV by producing antibodies. Immunoglobulin G (IgG) is the most abundant type of antibody and plays a significant role in long-term protection. When the body encounters VZV, through infection or vaccination, it begins to produce VZV-specific IgG antibodies a few weeks after exposure. The presence of VZV IgG in the bloodstream serves as immunological memory, confirming a successful defense against the virus. These IgG molecules circulate, ready to neutralize the virus upon subsequent exposure, conferring immunity. This test targets IgG, distinguishing it from Immunoglobulin M (IgM), which appears first during an acute or very recent infection and then fades away quickly.
When VZV IgG Testing is Ordered
A healthcare provider orders a VZV IgG test in specific clinical situations to assess a patient’s immunity, determined through a simple blood draw. Routine screening is necessary for healthcare workers and teachers who are likely to be exposed to the virus. Confirming immunity in these groups helps prevent outbreaks and protects susceptible patients. Pre-pregnancy screening is common, as a primary VZV infection during gestation can pose risks to the fetus. Testing is also performed before a patient begins immunosuppressive therapies, such as chemotherapy or organ transplantation. These treatments increase the risk of severe VZV infection or shingles reactivation. The test also confirms whether a person has developed immunity after receiving the varicella vaccine.
Interpreting Test Results
The VZV IgG test results are typically reported as Positive (or Reactive), Negative (or Non-Reactive), or Equivocal (or Indeterminate).
A Positive or Reactive result indicates that a significant level of VZV IgG antibody has been detected in the blood sample. This result confirms that the individual has protective immunity, either due to a past chickenpox infection or successful vaccination.
A Negative or Non-Reactive result means that no detectable VZV IgG antibodies were found in the blood sample. This finding indicates that the person is susceptible to VZV infection because they have not had prior exposure or the vaccine did not confer immunity. For non-immune adults and children, a healthcare provider will typically recommend vaccination to provide protection against chickenpox.
An Equivocal or Indeterminate result is assigned when the antibody level is too close to the cutoff threshold between positive and negative, making the result unclear. This borderline finding does not confirm immunity or susceptibility. It may occur during the early stages of a developing immune response. The recommended follow-up for an equivocal result is usually to repeat the blood test in 10 to 14 days.