TORCH Test

Blood may be tested from either the mother or the newborn infant to determine if the illness observed in the newborn is caused by one of these infections. A blood test can determine if the person has had a recent infection, a past infection, or has never been exposed to the virus. Patients with recent infection with one of the TORCH agents will have IgM antibody to the specific agent, and those with a past infection will have an IgG antibody, which is life-long. If neither immunoglobulin is detectable, there has been no infection with these microorganisms. In case of previous immunity of the mother, IgG antibody will always be present in the baby due to passive transfer through the placenta. However, IgM antibodies are too big to pass through the placenta, so their isolation in the baby blood will indicate a recent (or congenital) infection (see further information below).

The test is requested if a pregnant woman is suspected of having any of the TORCH infections. Rubella infection during the first 16 weeks of pregnancy presents major risks for the unborn baby. If a pregnant woman has a rash and other symptoms of rubella, laboratory tests are required to make the diagnosis. A physician cannot tell if a person has rubella by their clinical appearance since other infections may look the same. Women infected with toxoplasma or CMV may have flu-like symptoms that are not easily differentiated from other illnesses. Antibody testing will help the physician diagnose an infection that may be harmful to the unborn baby.

The test may also be requested on the newborn if the infant shows any signs suggestive of these infections, such as exceptionally small size relative to the gestational age, deafness, mental retardation, seizures, heart defects, cataracts, enlarged liver or spleen, low platelet level, or jaundice.

Results are usually given as positive or negative, indicating the presence or absence of IgG and IgM antibodies for each of these infectious agents (toxoplasma, rubella, CMV, and HSV). Presence of IgM antibodies in the newborn indicates high likelihood of infection with that organism. IgM antibodies produced in the mother cannot cross the placenta so presence of this type of antibody strongly suggests an active infection in the infant. Presence of IgG and absence of IgM antibody in the infant may reflect passive transfer of maternal antibody to the baby and does not indicate active infection in the baby.

Likewise, the presence of IgM antibody in the pregnant woman suggests a new infection with the virus or parasite. Further testing must be done to confirm these results since IgM antibody may be present for other reasons. IgG antibody in the pregnant woman may be a sign of past infection with one of these infectious agents. By testing a second blood sample drawn two weeks later, the level of antibody can be compared. If the second blood draw shows an increase in IgG antibody, it may indicate a recent infection with the infectious agent.

Use of the TORCH panel to diagnose these infections is becoming less common since more specific and sensitive tests to detect infection are available. However, some doctors still like the acronym to remember which tests to request. Relying on the presence of antibodies may delay the diagnosis since it takes days to weeks for the antibodies to be produced. Detection of the antigen or DNA (new modern test with amplification of viral genetic material) can be done earlier in the infectious process and are more specific.

A positive IgG antibody test is usually a sign of past exposure to the TORCH agent and is not a marker for current active infection. Detection of IgM antibody is more difficult, and false negative and false positive results may occur. Any positive results should be confirmed with additional specific tests before the diagnosis is considered valid. If your doctor suspects that you or your newborn may have one of these infections, even though the results were negative, other tests for the suspected infection should be done.