To screen for several infectious diseases that can cause birth defects in newborns and illness in adults
A blood sample is taken from a vein in the arm by needle or by heel prick for infants
TORCH is an acronym for a group of four infectious diseases that may cause illness in pregnant women and may cause birth defects in their newborns. The test is a screen for the presence of any of the antibodies to these infections. Confirmation of an active infection may require more specific tests.
The following tests make up the TORCH panel:
- Toxoplasmosis is a parasitic infection that can be passed from mother to baby through the placenta during pregnancy. An infection with Toxoplasma gondii can cause eye and central nervous system infections as well as brain and muscle cysts. If acquired during the pregnancy, it may result in a miscarriage or cause birth defects, though this depends on the time during the pregnancy in which the infection was acquired by the mother. Toxoplasmosis is acquired by ingesting the parasite when handling the excrement of infected cats, drinking unpasteurized goat’s milk, and, most commonly, by eating contaminated meat.
- Rubella is the virus that causes German measles. If contracted early in the pregnancy, the infant may develop heart disease, retarded growth, hearing loss, blood disorders, vision problems, or pneumonia. Problems that may develop during childhood include autism, brain problems, immune disorders, or thyroid disease.
- Cytomegalovirus (CMV) is another viral infection that the mother may have acquired. More than half of all American adults have been infected with CMV at some point in their life and, in most cases, it does not cause severe illness. It may pass to the foetus during pregnancy but can also infect newborns through breast milk. Most infected babies do not show any signs of infection at birth. Infected infants may have severe problems, such as hearing loss, mental retardation, pneumonia, hepatitis, or blood disorders.
- Herpes simplex virus (HSV) is a common viral infection. The two most common infections with HSV are “cold sores” affecting the lips and genital herpes. Both of these infections can recur. HSV is most commonly acquired through oral or genital contact. Newborns who contract the virus usually do so during travel through the birth canal of a woman who has a genital infection with HSV. The virus may spread throughout the newborn’s body, attacking vital organs. Treatment with specific antiviral medication should begin as soon as possible in the infected newborn. Even if treated, surviving babies may have permanent damage to the central nervous system. Mothers with recent or active genital herpes symptoms at the time of birth should inform the delivery staff.
How is the sample collected for testing?
A blood sample is required for the test. Blood can be collected by a heel prick from an infant or a needle is used to draw blood from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
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.
When is it requested?
The test is ordered 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 be ordered 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.
What does the test result mean?
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.
Is there anything else I should know?
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.
If I have a positive antibody test, does that mean I am infected?
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.
What type of testing is used to confirm infection with these microorganisms?
To make the diagnosis of an active infection with one of the TORCH agents, more specific confirmatory tests may be required. In a baby, cerebrospinal fluid testing (requiring a lumbar puncture or “spinal tap”) is often used to confirm toxoplasmosis, herpes and rubella; urine may be cultured for cytomegalovirus; and skin lesions may be scraped and cultured for herpes simplex virus. Making the diagnosis of toxoplasmosis in the pregnant woman or the baby may require additional blood samples, which are sent to a reference lab that specializes in this testing.