Although the four diseases are not particularly serious for adults who are exposed and treated, women who are become affected with any of these diseases during pregnancy are at risk for miscarriage, still birth, or for a child with serious birth defects and/or illness. Thus, this test is performed before or as soon as pregnancy is diagnosed to determine the mother's history of exposure to these organisms. The test is also performed on neonatal serum when the newborn presents with symptoms consistent with a congenitally acquired infection by one of the organisms above.
Precautions
TORCH screening can be associated with both false negative and false positive results. False negative IgM tests can result from IgG antibodies to the organism binding to the antigen used in the test or from immunodeficiency syndromes that reduce the antibody response to these organisms. False positive test results can result from rheumatoid, autoimmune, or heterophile antibodies in the mother's serum. When testing neonates, the IgG antibody levels may be detected as a result of prior infection or current maternal infection, and therefore does not mean the neonate is infected. Maternal antibodies to HSV and CMV may not adequately protect the fetus. TORCH screening requires blood from the mother and if needed, the neonate. The nurse or phlebotomist performing the venipuncture should observe universal precautions for the prevention of transmission of bloodborne pathogens.
Description
The TORCH panel is performed on women before or during pregnancy and on newborns if warranted by risk of infection during pregnancy. 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 make the blood flow more easily. The foot is then wiped with an alcohol swab and a lancet is used to stick the baby's heel on one side. Blood is collected from adults by venipuncture. The blood is collected by a nurse or phlebotomist from a vein located in the crease of the arm. Serum, the liquid portion of the blood after it clots, is used for the test.
When a person is infected with a pathogen, the normal immune response results in the production of immunoglobulin M (IgM) antibodies followed by immunoglobulin G (IgG) antibodies. IgM antibodies against TORCH organisms usually persist for about three months, while IgG antibodies remain detectable for a lifetime, providing immunity and preventing or reducing the severity of reinfection. Thus, if IgM antibodies are present in a pregnant woman, a current or recent infection with the organism has occurred. If IgM antibodies are absent and IgG antibodies are present and do not demonstrate an increase on serial testing several weeks later, it can be assumed that the person has had a previous infection by the corresponding organism, or has been vaccinated to prevent an infection. If the serum of a person has no evidence of either IgM or IgG antibodies specific for the organism, then the person is at risk of infection if exposed because they do not have any demonstrable immunity.
TORCH testing is most often performed by enzyme linked immunsorbent assay (ELISA). These are double antibody sandwich enzyme immunoassays in which the antigens or organisms are bound to a solid phase such as the bottom of a plastic well. Dilutions of the patient's serum are prepared and incubated with the antigens. Any specific antibodies to the antigen will bind forming antibody-antigen complexes. The wells are washed to remove unbound serum proteins, and enzyme-conjugated antihuman immunoglobulin is added. The wells are washed again to remove any unbound reagent antibody and a substrate is added. If antibodies to the organism are present, the enzyme converts the substrate to a colored product that can be measured. Assays for IgM or IgG antibodies are available. Alternative procedures include latex agglutination, indirect immunofluorescence assay for toxoplasma antibodies, chemiluminescence immunoassay, DNA amplification, and viral culture.
The TORCH panel is used to determine the immune status of a pregnant female for Toxoplasma gondii, rubella, cytomegalovirus, and herpes simplex virus. If IgG antibodies are present at a concentration that indicates immunity against each of these organisms, the female is in no danger of contracting a toxoplama or rubella infection during pregnancy and transmitting it to the fetus. In addition, there is a low probability of transmitting a herpes simplex or CMV infection although the antibodies detected by the test may not be fully protective. If antibodies are absent, the patient will be observed closely during the pregnancy for any sign of suspected infection. Should an infection occur, it will need to be treated aggressively to prevent transmission to the fetus.
The organisms which comprise the TORCH panel are commonly encountered. Most people are exposed the them during childhood. In most healthy persons exposed to Toxoplasma gondii, the organism causes an asymptomatic infection or mild self-limiting illness resembling infectious mononucleosis. The same pattern occurs for CMV infection. Rubella causes an acute infection with fever and rash, but is self-limiting with symptoms subsiding in two to three days. Children and young adults are typically infected. Herpes simplex 1 typically causes fever blisters. The infections caused by TORCH organisms are grouped together because they may all result in stillbirth or serious birth defects when transmitted from an infected mother to her fetus during pregnancy.
The symptoms of the TORCH infections in neonates include:
This group of defects is called the TORCH syndrome. As such, other organisms causing serious congenital infections such as syphilis, human immunodeficiency virus, parvovirus, and enterovirus are sometimes considered part of this group. A newborn baby with these symptoms will be given a TORCH test and may be tested for some of these other infections as well.
In addition to these symptoms, each of the TORCH infections has its own characteristic symptoms in newborns.
Toxoplasmosis
Toxoplasmosis is caused by Toxoplasma gondii, a parasite that can acquired from ingesting cysts from the feces of infected cats, drinking unpasteurized milk, or eating contaminated meat containing the cyst or trophozoites. The infection is transmitted to the infant through the placenta, and can cause eye deformity, eye infections and mental retardation by invading brain tissue. The later in pregnancy the mother is infected, the higher the probability that the fetus will be affected. On the other hand, toxoplasmosis exposure early in pregnancy is more likely to cause a miscarriage or serious birth defects. The incidence of toxoplasmosis in newborns is between one to eight per 1,000 live births in the United States.
Rubella
Prior to the 1970s the incidence of congenital rubella infection was approximately 6.3 per 10,000 births. Ten years following the introduction of the vaccine the rate dropped six-fold to approximately one in 10,000 births. The rate of fetal infection varies depending on when in gestation the exposure occurred. Approximately 85% of neonates who develop birth defects as a result of infection during pregnancy contract the virus during the first eight weeks of gestation. Infants born with rubella may show signs of heart disease, retarded growth, ocular defects, or pneumonia at birth. They may also develop problems later in childhood, including autism, hearing loss, brain involvement, immune system disorders, or thyroid disease.
Cytomegalovirus
Cytomegalovirus belongs to the herpes virus group of infections. It can be transmitted through body secretions, as well as by sexual contact; some newborns acquire CMV through breast milk. Of newborns in the
United States infected with CMV, 10% will have measurable symptoms. The mortality rate for these symptomatic newborns is 20-30%. Surviving infants with CMV may suffer from hearing loss (15%) or mental retardation (30%). Newborns that acquire CMV during the birth process or shortly after birth may develop pneumonia, hepatitis, or various blood disorders.
Herpes simplex virus
Herpes virus infections are among the most common viral infections in humans. They are spread by oral, as well as genital, contact. It is estimated that between one in 1,000 and one in 5,000 infants are born with HSV infections. About 80% 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% will have localized infections of the eyes, mouth, or skin. About 50% of infected infants will develop disease spread 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%. Even with antiviral medication, the mortality rate is still 15-20%, with 40-55% of the survivors having long-term damage to the central nervous system. It is critical for the doctor to diagnose HSV infection in the newborn as soon as possible, for effective treatment.
TORCH testing is most effectively utilized to determine the mother's immune status and monitor those
pregnant females who do not demonstrate immunity. TORCH testing of neonates is difficult to evaluate, since maternal IgG from either present or past exposure crosses the placenta and will often produce higher levels in the neonate than in maternal serum. The infant's IgM response may or may not be developed sufficiently at birth to be definitive, and false positive and negative results are known to occur. When neonates are tested, the TORCH screen should include testing for specific IgM antibodies, and should be repeated within two to three weeks to demonstrate a rise in concentration indicative of active infection. Viral cultures or DNA probe tests are required to make a definitive diagnosis of the specific infection. CMV can be cultured from urine and white blood cells; herpes simplex can be cultured from vesicles on the skin or conjunctiva (mucus membranes inside the eyelids); both CMV and rubella may be cultured from cerebrospinal fluid, but culture time for rubella can take several weeks. Cultures are performed by inoculating living cells such as primary monkey kidney.
Preparation
No special preparation, other than sterile technique, is required.
Aftercare
There is no special aftercare specific to the test itself. Discomfort or bruising may occur at the puncture site, or the person may feel dizzy or faint. Pressure to the puncture site until the bleeding stops reduces bruising. Applying warm packs to the puncture site relieves discomfort.
Complications
For the mother, minor temporary discomfort may occur with any blood test, but there are no complications specific to TORCH testing. For the infant, complications associated with the TORCH test are those resulting from the heelstick technique/venipuncture. These risks include scarring, infection, cellulitis (inflammation of cellular tissue), and small lumpy calcium deposits. Results of serological tests (antibody tests) on the neonate may be inconclusive. Follow-up testing may be needed to demonstrate a rise in antibody titre (concentration). Additional diagnostic testing and/or treatment is determined on a case-by-case basis, depending on results.
Results
A normal result is undetectable IgM antibody in the blood of either mother or neonate. The presence of IgM indicates recent or current infection. When specific IgM antibodies to TORCH antigens are found in the neonate, this indicates a very high probability of infection with the respective organism, and should be followed up by subsequent testing to demonstrate either a rise in titre or by viral culture or DNA tests.
For rubella and Toxiplasma gondii, the presence of a significant IgG titer in maternal serum indicates immunity for both mother and fetus. The presence of IgG antibody to CMV and herpes simplex in maternal serum may or may not be fully protective. When neonatal infection is suspected, TORCH testing of the neonate may not be definitive. IgG antibodies in fetal serum may result from either current or prior maternal infection or vaccination. In such cases, an IgM level should be measured in both maternal and neonatal serum, and viral cultures or DNA testing should be performed.
Results for TORCH antibodies may be interpreted as negative, equivocal, or positive. Equivocal results occur when antibody levels fall within an index value below the low positive standard but above the negative standard. Testing by another method is recommended. In addition, serum from the patient should be collected and retested after waiting an additional 10-14 days.
Health care team member roles
The test is typically ordered and interpreted by a physician. Blood samples for the TORCH screen are collected by a nurse or phlebotomist. Pregnant women found to be exposed should receive treatment and a thorough explanation of potential consequences by their obstetrician. Counseling may be helpful. TORCH testing is performed by a clinical laboratory scientist/medical technologist.
KEY TERMS
Antibody—A protein molecule produced by the immune system that is specific to a disease agent, such as CMV. The antibody combines with the antigen on the organism and facilitates its destruction or removal from the host.
Perinatal—Referring to the period of time surrounding an infant's birth, from the last two months of pregnancy to the first 28 days of life. The TORCH panel tests for perinatal infections.
Small-for-gestational-age (SGA)—A term used to describe newborns who are below the 10th percentile in height or weight for their estimated gestational age. The gestational age is based upon the date of the mother's last menstrual period. SGA is one of the symptoms of TORCH syndrome.
Titre (titer)—The concentration of a substance in a given sample of blood or other tissue fluid.
BOOKS
Cruse, Julius M., and Robert E. Lewis. Illustrated Dictionary of Immunology. New York: CRC Press, 1995.
"Pediatrics and Genetics: Disturbances in Newborns and Infants." In vol. II, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
"Procedures: Heelstick (Capillary Blood Sampling)." In Neonatology: Management, Procedures, On-Call Problems, Diseases, and Drugs. 4th edition. Edited by Tricia Lacy Gomella, et al. Norwalk, CT: Appleton & Lange, 1999.
OTHER
Pittsburgh.com. Illustrated Health Encyclopedia. <http://www.pittsburgh.com/shared/health/adam/ency/article>.
