The TORCH test is used to screen pregnant women and newborns for antibodies to the infectious diseases included in the panel, if either the mother or newborn has symptoms. The blood test can determine if the person has had a recent infection, a past infection, or has never been exposed.
The test is ordered when a pregnant woman is suspected of having any of the TORCH infections. These infections can be serious if they occur during pregnancy because they can cross the placenta from the mother to the developing fetus and can cause congenital defects in the newborn.
Rubella infection during the first 16 weeks of pregnancy presents major risks for the unborn baby. When 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 be ordered on the newborn when the infant shows any signs suggestive of these infections, such as:
Exceptionally small size relative to the gestational age
Results are usually given as positive or negative, indicating the presence or absence of IgG and IgM antibodies for each of the infectious agents tested for with the panel. A "normal" result is negative (undetectable) IgM antibody in the blood of the mother or newborn.
Presence of IgM antibodies indicates either a current or recent infection. A positive IgM result in a 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 an infant may reflect passive transfer of maternal antibody to the baby and does not indicate active infection in that infant.
Likewise, the presence of IgM antibody in a 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. 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 growing the microorganism in culture can be done earlier in the infectious process and are more specific. Some recent studies have found questionable benefit to routine TORCH screening in newborns with certain symptoms, such as being small for gestational age, and greater benefit to using more specific methods, such as, in this example, CMV culture.
This article was last reviewed on July 20, 2011. | This article was last modified on June 4, 2014.
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