What this test measures
IgM antibodies for the 5 classical TORCH infections — IgM rises within 1–3 weeks of primary infection and can persist for months. False positives are common (especially toxoplasma and CMV IgM), so a reactive IgM almost always requires confirmation by paired IgG with avidity testing, PCR, or follow-up serology.
Why it matters
IgM-only TORCH is less useful than the combined IgM + IgG panel — without IgG context, an isolated positive IgM is hard to interpret. Indications: suspected acute infection in pregnancy (fever, rash, lymphadenopathy, abnormal ultrasound), recent travel to high-risk areas, contact with sick children, or follow-up of equivocal IgG seroconversion.
How to prepare
No fasting required. Disclose pregnancy stage, recent illness symptoms (fever, rash, lymphadenopathy), travel history, raw-meat or cat-litter exposure, contact with chickenpox / measles / rubella.
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 |
|---|---|---|---|
| TORCH IgM Components (reactive / non-reactive)[1][2] | Non-reactive | Negative — no recent infection for that organism. Doesn't rule out very early window (< 2 weeks). | Positive — possible recent / acute infection. Confirm with: paired IgG seroconversion, IgG avidity (low = recent, high = old), PCR (especially for CMV in amniotic fluid). Persistent IgM is common with toxoplasma and CMV — don't treat solely on positive IgM. |
IgM-positive — what to do
| Marker | IgM positive — next step |
|---|---|
| Toxoplasma | IgG avidity; PCR amniotic fluid if high suspicion |
| Rubella | IgG seroconversion; PCR if exposed; counsel on CRS risk |
| CMV | IgG avidity; PCR amniotic fluid; consider hyperimmune globulin |
| HSV-1 / 2 | PCR lesion if active ulcer; serology rarely diagnostic alone |
Frequently asked questions
Why is IgM tricky?
IgM can persist for months after primary infection (especially toxoplasma) and false positives are common. Isolated IgM positivity without IgG context is hard to act on.
Why is IgG avidity helpful?
IgG avidity matures over months — low-avidity IgG suggests recent infection (last 3-4 months), high-avidity suggests older. Combined with IgM, it distinguishes recent from past infection.
My CMV IgM is positive in pregnancy — what now?
Order IgG and IgG avidity. Low avidity + IgM positive = recent primary infection; counsel on fetal risk (30% transmission, 20% sequelae). Amniotic fluid PCR can confirm fetal infection. Hyperimmune globulin is being investigated but not standard of care.
Should I get IgM-only without IgG?
Generally no — IgG context is essential for interpretation. The combined 8-marker panel (IgM + IgG) is more informative.
What is congenital rubella syndrome?
CRS occurs when rubella infection in first trimester crosses the placenta — causing cataracts, congenital heart disease, deafness, microcephaly, intellectual disability. Now rare with widespread MMR vaccination.
Related Immunology tests
Tests commonly ordered alongside TORCH-5 IgM, or that help interpret an unexpected result.
Sources & references
- RCOG — Antenatal Infection Screening · accessed 2026-05-30T00:00:00.000Z
- CDC — TORCH Infections · accessed 2026-05-30T00:00:00.000Z
- FOGSI — Antenatal Care · accessed 2026-05-30T00:00:00.000Z
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