The TORCH test, sometimes called the TORCH panel, belongs to a category of blood tests called infectious-disease antibody titers. A titer is the serial dilution of antibodies (protein molecules or immunoglobulins produced by the immune system in response to specific disease agents) found in blood serum that determines their level of concentration. Antibodies are proteins produced by the immune system in response to infectious agents that are foreign to the body, such as viruses, bacteria, parasites, or toxins. These infectious organisms have antigens on their surfaces that stimulate the immune system to produce corresponding antibodies. IgM antibodies are produced in response to viruses. The TORCH test screens for the presence of IgM antibodies, and the titer determines their concentration in the blood. The name of the test is an acronym derived from the initial letters of the five groups of chronic infections: toxoplasmosis , other viruses, rubella , cytomegalovirus (CMV), and herpes simplex virus (HSV). The "other viruses" usually include syphilis, hepatitis B , coxsackie virus, Epstein-Barr virus (mononucleosis), varicella-zoster virus, and human parvovirus. The test is performed by various methods in the clinical laboratory and may also be referred to as viral immunoglobulins testing. Methods used in the early 2000s are more sensitive and specific and can identify the specific virus.
A TORCH test is performed to help screen for certain virus infections in infants who may have been exposed to a causative organism. The five groups of disease-causing organisms whose antibodies are measured by the TORCH test are grouped together because they can cause a cluster of symptomatic birth defects in newborns. This group of defects is sometimes called the TORCH syndrome. The pediatrician may order the TORCH test to be performed when a newborn has these symptoms, in order to determine if any of the five types of infection may be involved.
Symptoms of TORCH syndrome that may encourage testing include the following:
- Small size in proportion to length of the mother's pregnancy at time of delivery: Infants who are smaller than would be expected (below the tenth percentile) are referred to as small-for-gestational-age (SGA).
- Enlarged liver and spleen.
- Low level of platelets (tiny cellular elements in blood that are an important part of coagulation).
- Skin rash: The type of skin rash associated with the TORCH syndrome is usually reddish-purple or brown and is caused by the leakage of blood from broken capillaries into the baby's skin.
- Central nervous system impairment: This may include encephalitis , calcium deposits in brain tissue, or seizures.
- Jaundice : Yellow-stained skin and whites of the eyes due to elevated levels of bilirubin, a substance normally filtered out by the liver. Jaundice may indicate liver dysfunction, although it can also be a normal result of red cell turnover in the newborn.
Besides general symptoms that may encourage a pediatrician to order the TORCH panel of tests, each of the TORCH infections has its own origins and may have a characteristic cluster of symptoms in newborns. These unique characteristics, the general condition and symptoms of the child, and the test results are studied in order for the physician to make a diagnosis.
Toxoplasmosis is caused by Toxoplasma gondii , a parasite that can be acquired by the mother from handling cat feces, drinking unpasteurized milk, or eating contaminated meat. The infection is carried to the infant through the mother's placenta and can cause impairment of the infant's eyes (opthalmic impairment) and central nervous system (neurological dysfunction). The organism can invade brain or muscle tissue and form cysts. Infection acquired by the mother later in pregnancy usually decreases the likelihood of infection in the infant at birth although eye problems may occur in adolescence . Toxoplasmosis early in pregnancy is more likely to cause miscarriage or serious birth defects. The incidence of toxoplasmosis in newborns is one in 1,000 live births.
Other viruses (syphilis)
Syphilis is caused by the spiral- or coil-shaped bacteria (spirochete), Treponema pallidum . It is transmitted among adults through sexual intercourse. About 2 to 5 percent of children born to mothers diagnosed with syphilis have the disease at birth. Syphilis was added to the TORCH panel because of an increase in reported cases after 1990. Syphilis can cause early delivery, miscarriage, and is a potentially life-threatening infection for an affected fetus, often resulting in stillbirth. The mortality rate in infants infected with syphilis is about 54 percent.
Rubella is a virus that has a seasonal pattern, with epidemics most likely in the spring. Between 0.1 to 2 percent of newborns are infected with rubella. The rate of fetal infection varies according to the timing of the mother's infection during pregnancy. Birth defects, however, are most likely (85%) in infants infected during the first eight weeks of pregnancy. Infants born with rubella may already show signs of heart disease, retarded growth, hearing loss, blood disorders, vision problems, or pneumonia . They may also develop problems later in childhood, including autism , hearing loss, brain syndromes, immune system disorders, or thyroid disease.
Cytomegalovirus belongs to the herpesvirus group of infections. It can be transmitted through body secretions, as well as by sexual contact; some newborns acquire CMV through the mother's breast milk. In adults, it produces symptoms resembling those of mononucleosis. About 1 to 2.2 percent of newborns in the United States are infected with CMV. Of this group, 10 percent have measurable symptoms. The mortality rate for these symptomatic newborns is 20 to 30 percent. Surviving infants with CMV may suffer from hearing problems (15%) or mental retardation (30%). Newborns who acquire CMV during the birth process or shortly after birth may develop pneumonia, hepatitis, or various blood disorders.
Herpes simplex virus (HSV)
Herpesvirus infections are among the most common viral infections in humans. They are spread by oral or genital contact. It is estimated that between one in 1,000 and one in 5,000 infants are born with HSV infections. About 80 percent of these infections are acquired during the birth process itself; the virus enters the infant through its eyes, skin, mouth, and upper respiratory tract. Of infants born with HSV infection, about 20 percent have localized infections of the eyes, mouth, or skin. About 50 percent of infected infants will develop the disease throughout the body (disseminated) within nine to 11 days after birth. Disseminated herpes infections attack the liver and adrenal glands, as well as other body organs. Without treatment, the mortality rate is 80 percent. Even with antiviral medication, the mortality rate is still 15 to 20 percent, with 40 to 55 percent of the survivors having long-term damage to the central nervous system. In order to begin early, effective treatment, it is critical for pediatricians to diagnose HSV infection in newborns as soon as possible.
Performing the TORCH panel requires obtaining a sample of the infant's blood. Samples from infants are usually obtained by the heelstick procedure when only a small quantity of blood is needed. The baby's foot is wrapped in a warm cloth for five minutes to bring blood to the surface and help it to flow more easily. The foot is then sterilized with an alcohol swab and a lancet is used to puncture the baby's heel on one side, avoiding the center of the heel to prevent inflammation of the bone. The blood sample is drawn in tiny capillary tubes, properly labeled, and taken to the laboratory for testing. In rare instances, a phlebotomist is not able to draw sufficient blood from a heel puncture, and a physician may draw venous blood from a femoral vein in the groin area or another vein larger than veins in an infant's arms.
Since the TORCH test is a screening or first-level test, the pediatrician may order tests of other body fluids or tissues to confirm the diagnosis of a specific infection. In suspected cases of toxoplasmosis, rubella, or syphilis, cerebrospinal fluid may be obtained from the infant by spinal tap in order to confirm the diagnosis. A diagnosis of CMV is usually confirmed by culturing the virus in a sample of the infant's urine. In HSV infections, tissue culture is the best method to confirm the diagnosis.
Because toxoplasmosis can be transmitted by handling cat feces, pregnant women should avoid cleaning cat boxes or handling cats. Any suspected infection should be reported to the obstetrician so that testing for the causative parasite in the mother can be performed.
Medical personnel and family members must be aware of the possible presence of infective organisms in the infant and proper precautions taken, such as hand washing, when the infant or the infant's body fluids (blood, urine, feces) are handled.
If the infant has had blood drawn often from the same site on the heel or heels, causing scarring, inflammation, or the accumulation of tissue fluid, it may cause inaccurate test results.
False negative and false positive results can occur with the TORCH test for immunoglobulins because of cross-reacting antibodies, especially among the different types of herpes viruses.
No special preparation, other than sterile technique by medical personnel, is required.
The site from which blood is withdrawn must be kept clean after the procedure and must be checked regularly for bleeding. A small adhesive patch may be used to protect the site.
The performance of the TORCH test carries no significant risk. Drawing blood for the test may involve light bleeding or bruising at the site of puncture or blood may accumulate under the puncture site (hematoma), requiring that a new location be found for subsequent tests. The infant's heel may be at risk of scarring, infection of the bone, cellulitis (inflammation of cellular tissue), small lumpy calcium deposits.
The normal result of a TORCH panel reveals normal levels of immunoglobulin M (IgM) antibody in the infant's blood. IgM is one of five types of antibodies (protein molecules) produced by the immune system and found in blood. IgM is a specific class of antibody that seeks out virus particles. It is the most common type of immunoglobulin in newborns and, therefore, the most useful indicator of the presence of one of the TORCH virus infections.
The general abnormal or "positive" result reveals high levels of IgM antibody present in the infant's blood. The test can be refined further for antibodies specific to given disease agents. The TORCH screen, however, can produce both false-positive and false-negative findings. Doctors can measure IgM levels in the infant's cerebrospinal fluid, as well as in the blood, if confirmation is needed.
Parents will necessarily be concerned about the possibility of infection in the child and the amount of testing that may have to be done. Awareness of the value of the TORCH panel of tests to help confirm the presence of an infective organism and its concentration in the blood is important, especially because confirmatory tests lead to faster, more effective treatment. Medical personnel can teach parents about safe practices for handling an infant with a virus infection that can possibly spread to family members.
Antibody —A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.
Antigen —A substance (usually a protein) identified as foreign by the body's immune system, triggering the release of antibodies as part of the body's immune response.
Bacteria —Singular, bacterium; tiny, one-celled forms of life that cause many diseases and infections.
Titer —The highest dilution of a material (e.g., serum or other body fluid) that produces a reaction in an immunologic test system. Also refers to the extent to which an antibody can be diluted before it will no longer react with a specific antigen. Also spelled titre.
Virus —A small infectious agent consisting of a core of genetic material (DNA or RNA) surrounded by a shell of protein. A virus needs a living cell to reproduce.
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Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.
"TORCH Test." Joseph F. Smith Medical Library. Available online at http://www.chclibary.org/micromed/00068480.html (accessed December 2, 2004).
L. Lee Culvert Rebecca J. Frey, PhD