Cytomegalovirus IgG (CMV IgG)
An antibody test showing whether a person has been infected with cytomegalovirus (CMV) in the past. A positive IgG is very common and usually means past exposure and immunity. Its main practical use is checking immune status before pregnancy, transplant, or when donating blood or organs.
What it measures
Cytomegalovirus is a widespread herpesvirus that most people catch at some point, often with no symptoms, after which it stays dormant in the body for life. CMV IgG is the antibody that reflects this past exposure: once someone has been infected, IgG becomes positive and generally stays positive permanently, marking immunity. A large proportion of adults are CMV IgG positive, so the result on its own is usually unremarkable. Its value comes in specific situations. In pregnancy, knowing a woman's CMV status matters because a first (primary) infection during pregnancy can affect the baby — so IgG is checked, often alongside IgM (which suggests a recent or current infection) and, if needed, an avidity test to date the infection. Before organ or bone-marrow transplant, the CMV status of both donor and recipient guides prevention, because CMV can reactivate and cause serious illness in people with weakened immunity. It is also used in blood and organ donation. So CMV IgG is less a test of illness than a marker of prior exposure and immune status, interpreted according to the setting.
What a high value can mean
- Positive CMV IgG — past exposure to CMV and, in a healthy person, immunity; a very common result.
- Positive IgG with positive IgM — suggests a recent or current infection; timed with an avidity test if it matters (e.g. in pregnancy).
- CMV status in transplant or immune-weakened patients — guides prevention and monitoring for reactivation.
What a low value can mean
- Negative CMV IgG — no past exposure; the person is susceptible to a first infection.
- A negative result in pregnancy — means counselling on avoiding infection, as a primary infection then carries risk to the baby.
- A negative result in a transplant recipient with a positive donor — a high-risk combination that guides preventive treatment.
When to discuss with a doctor
CMV IgG is used to establish immune status rather than to diagnose a passing illness. Its key uses are in pregnancy (a first CMV infection during pregnancy can affect the baby, so IgG, IgM and sometimes an avidity test are interpreted together), and before or after organ and bone-marrow transplant (where CMV can reactivate dangerously in people with weakened immunity, so donor and recipient status guides prevention). In a healthy person outside these settings, a positive IgG simply reflects common past exposure and immunity and needs no action. Because the interpretation is so context-dependent, it is read with the clinical situation. Mediora.AI shows CMV IgG alongside the related markers so the exposure and immune-status pattern is visible; interpretation for pregnancy or transplant belongs with your doctor.