How to interpret TORCH investigations. A short guide.

1. There are 2 Types of Antibodies which we need to test for. IgG and IgM.

2.IgM Antibodies:

  • appear immediately after an infection, usually persist for 10-12 weeks.
  • MAY PERSIST for 1-2 YEARS. Every IgM doesn’t mean a recent infection
  • IgM does NOT mean fetal infection. Further workup is needed

3.IgG Antibodies:

  • IgG Antibodies appear after around 2 weeks, start falling after 2 months but Persist LIFELONG


No exposure to infection : IgM, IgG Negative

Acute infection: IgM, IgG

Past infection : IgM Negative, IgG

So is this enough to diagnose TORCH infections?

We have another weapon in our arsenal of tests.

4.IgG Avidity:

Measures the binding AFFINITY of the IgG Antibody After infection.

The affinity increases over time.

A recent infection : LOW AVIDITY

A Past infection : HIGH AVIDITY since the antibodies have been around for some time. They have developed a strong affinity i.e avidity. Avidity, in most cases but not all, shifts from low to high after about 5 months. If the avidity is high, this suggests infection occurred at least 5 months before testing

Let’s look at a few clinical cases.

CASE 1:25 year old Woman with a history of 2 prior abortions is advised a TORCH test. She is currently 8 weeks pregnant

The Results are as follows:

1.Rubella IgG, IgM -ve

2.CMV IgG, IgM -ve

3.Toxo IgG IgM : ve

What is to be done next?

If acute infection is suspected, repeat (TORCH) testing is recommended within 2 to 3 weeks. A 4-fold rise in IgG antibody titres between tests indicates a recent infection

Then, A Toxo IgG Avidity is advised.


Avidity is LOW

This means that the Infection is more recent.

Spiramycin is the treatment of choice.

USG is advised for fetal anomalies

Amniocentesis is advised in the 2nd TMP to detect fetal infection

Regular monitoring by USG

There are 10-20% chances of infection of fetus

Out of these infections approximately half can be severe.

Serologic screening in pregnant women should be done only if they are at risk for primary Toxoplasma gondii infection.

Toxoplasma gondii infection should be suspected and screening should be offered to pregnant women with ultrasound findings consistent with possible TORCH (toxoplasmosis, rubella, cytomegalovirus, herpes, and other) infection, including but not limited to intracranial calcification, microcephaly, hydrocephalus, ascites, hepatosplenomegaly, or severe intrauterine growth restriction.

Here is a short flow chart for TOXO Investigations

CASE 2: 26 year old female with a history of recurrent abortions

Toxo IgG, IgM Positive.

Can Toxoplasmosis be responsible for recurrent abortions?

No, it cannot. It can only cause sporadic infections.

The reason being that after an episode of Toxoplasmosis, the woman becomes immune. She is unlikely to be infected unless she has comorbidities and is immunocompromised

CASE 3: 32 Year old 8 weeks pregnant

Rubella IgG , IgM -: She is protected from infection and is at no risk for Rubella Infection. Reassure the patient.

On the other hand, if the IgG is negative, we must educate the woman on the signs and symptoms of rubella.

Clinical symptoms appear after the incubation phaseof 13-20 days, and are characterized by lymphadenopathy, maculopapular rash and fever.

In some cases, there is arthralgia (30% of adults), encephalitis (1 case out of 10 000) with good prognosis and thrombocytopenia. After a primary infection, adults have long-term immunity, but sometimes, it is possible to have a new infection. The incidence of this type of re-infection during pregnancy is not known.

It is important to determine the immune status of women of childbearing age, preferably before pregnancy, to vaccinate those who are seronegative.

If no determination has been performed prior to conception, it should be carried out as soon as pregnancy is confirmed to ensure monitoring of women who are not immune

CASE 4: 30 Year old with 12 weeks gestation



Primary infection or a reactivation of a latent infection

Perform CMV IgG Avidity:

High: Reactivation

Low: Primary Infection

Here is a short flow chart for CMV infections


  • Women with past Toxoplasmosis or Rubella are unlikely to have a recurrent infection.
  • Reinfectionrecurrences are more likely with CMV and HSV
  • TORCH infections are don’t cause recurrent ABORTIONS. They can explain sporadic events.
  • Vaccination against Rubella is important. If Rubella status is not clear. Administer vaccine and wait for 1-2 months before planning.
  • Testing of TORCH should be in a reference lab with us of IgG Avidity.
  • Maternal infection doesn’t always mean a fetal infection.
  • Further testing with USG,Amniocentesis in the 2nd TMP is important
  • If Toxo IgG,M is , Advise repeat testing in 2-3 weeks.
  • Then perform Avidity. If avidity is low, this could mean a recent infection. This still needs to be confirmed with USG and amniocentesis in the 2nd TMP.
  • A Toxo IgG result with a IgM -ve does not warrant treatment.
  • A Rubella IgG Positive with IgM -ve is not at risk of Rubella.
  • For Rubella: Carry out an IgM assay in the following cases:
  • • possible contact with the disease, • if clinical symptoms suggest primary infection, • seroconversion or if raised IgG levels are observed during systematic checks
  • If USG shows signs of TORCH infection, Diagnostic tests are important in First TMP

I’d love to know your experiences in using this test in clinical scenarios. Feel free to comment on the same.

Dr.Ajay Phadke MD

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