What this test measures
CMV IgG is the immunoglobulin-G antibody against cytomegalovirus (CMV, human herpesvirus 5). It typically appears 2–4 weeks after primary infection and persists for life. A positive IgG indicates that the immune system has encountered CMV at some point.
Like other herpesviruses, CMV establishes lifelong latent infection. IgG positivity confirms past exposure but does not distinguish remote past infection from reactivation. CMV IgG avidity testing (low avidity = recent infection; high avidity = old infection) is sometimes used to estimate timing in pregnancy.
Why it matters
India has high CMV seroprevalence — 80–95% of adults are IgG-positive, reflecting near-universal childhood exposure. CMV is usually asymptomatic in immunocompetent adults but matters in three key clinical contexts:
1. **Pregnancy**: Primary maternal CMV infection in pregnancy can cause congenital CMV in the baby — the leading non-genetic cause of sensorineural hearing loss and developmental delay. IgG positivity before pregnancy means past infection (lower but not zero risk to future babies).
2. **Transplant**: CMV serostatus of donor and recipient determines transplant CMV risk. D+/R− (donor positive, recipient negative) is highest risk; prophylactic antivirals are standard.
3. **Immunosuppression / HIV**: CMV reactivation causes severe disease — retinitis, colitis, pneumonitis — in HIV with low CD4, transplant patients, and those on chemotherapy.
How to prepare
No fasting required. Mention pregnancy, immunosuppression, transplant status, or HIV status — these change interpretation and follow-up.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-CMV IgG (AU/mL or Index / Reactive-Non-reactive)[1][2] | Reactive in 80–95% of Indian adults | Non-reactive — no past CMV infection. Susceptible to primary infection. In pregnancy, special caution and possibly repeat testing in each trimester to detect seroconversion. In transplant recipients, D+/R− status carries higher post-transplant CMV risk. | Reactive — past CMV exposure. In immunocompetent adults, no action needed. In pregnancy, indicates past infection (lower risk for the current baby). In immunosuppressed patients, watch for reactivation with CMV DNA PCR if symptoms develop. |
CMV IgG and IgM — interpreting together
| IgG | IgM | Interpretation |
|---|---|---|
| Positive | Negative | Past CMV infection — latent, no current activity. |
| Positive | Positive | Recent primary infection or reactivation. IgG avidity helps date in pregnancy. |
| Negative | Positive | Early primary infection — IgG should follow in 2–4 weeks. |
| Negative | Negative | Never infected — susceptible. |
Frequently asked questions
I am pregnant and my CMV IgG is positive. Is my baby safe?
Positive IgG before pregnancy means past infection — risk of congenital CMV is lower (<2%) but not zero. Reactivation or reinfection can still occur. Avoid CMV exposure (close contact with toddlers' saliva/urine) and discuss with your obstetrician.
My IgG is negative. What should I do during pregnancy?
You are at risk of primary CMV infection. Hand hygiene after handling toddlers (saliva, nappies), avoid sharing cutlery/utensils with young children, and discuss repeat IgG testing in each trimester with your obstetrician.
Why is CMV serostatus important in transplant?
CMV is one of the leading post-transplant infections. D+/R− (donor positive, recipient negative) is the highest risk — prophylactic valganciclovir is standard. R+ patients (any donor) need monitoring for reactivation.
I have HIV and am IgG-positive. Should I worry?
Risk of CMV reactivation rises sharply when CD4 drops below 50. CMV retinitis, colitis, and pneumonitis are the main concerns. Routine fundoscopy and prompt CMV DNA PCR for symptoms are recommended.
How does CMV spread?
CMV spreads through saliva, urine, blood, sexual contact, breast milk, and transplacentally. Young children are common asymptomatic shedders — a key concern for pregnant carers.
Is there a CMV vaccine?
No licensed vaccine yet, though candidates are in clinical trials. Prevention is hygiene-based.
Does positive IgG mean lifelong protection?
IgG indicates past exposure and latency. It does not prevent reactivation under immunosuppression, but it does reduce primary infection risk during pregnancy.
Related Infectious Disease tests
Tests commonly ordered alongside CYTOMEGALO VIRUS (CMV) - IgG, or that help interpret an unexpected result.
Sources & references
- CDC — Cytomegalovirus · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — CMV Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Cytomegalovirus · accessed 2026-05-30T00:00:00.000Z
- IAP — Indian Academy of Pediatrics, Congenital CMV · accessed 2026-05-30T00:00:00.000Z
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