The TORCH test, which is sometimes called the TORCH panel, belongs to a category of blood tests called infectious-disease antibody titer tests. This typeof blood test measures the presence of antibodies (protein molecules producedby the human immune system in response to a specific disease agent) and their level of concentration in the blood. The name of the test comes from the initial letters of the five disease categories. The TORCH test measures the levels of an infant's antibodies against five groups of chronic infections: Toxoplasmosis, Other infections, Rubella, Cytomegalovirus (CMV), and Herpes simplex virus (HSV). The "other infections" usually include syphilis, hepatitis B,coxsackie virus, Epstein-Barr virus, varicella-zoster virus, and human parvovirus.
Since the TORCH test is a screening or first-level test, the pediatrician mayorder tests of other body fluids or tissues to confirm the diagnosis of a specific infection. In the case of toxoplasmosis, rubella, and syphilis, cerebrospinal fluid may be obtained from the infant through a spinal tap in order to confirm the diagnosis. In the case of CMV, the diagnosis is 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.
The five categories of 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. A newborn baby with these symptoms will be given a TORCH test to seeif any of the five types of infection are involved. The symptoms of the TORCHsyndrome include:
- Small size in proportion to length of the mother'spregnancy at time of delivery. Infants who are smaller than would be expected(below the 10th percentile) are referred to as small-for-gestational-age, orSGA.
- Enlarged liver and spleen
- Low level of platelets in the blood
- Skin rash. The type of skin rash associated with the TORCHsyndrome is usually reddish-purple or brown and is caused by the leakage of blood from broken capillaries into the baby's skin.
- Involvement of the central nervous system. These defects can include encephalitis, calcium deposits in the brain tissue, and seizures.
- Jaundice. The yellowish discoloration of the skin and whites of the eyes due to liver disease.
In addition to these symptoms, each of the TORCH infections has its own characteristic symptom cluster in newborns:
The normal result would be normal levels of immunoglobulin M (IgM) antibody in the infant's blood. IgM is one of five types of protein molecules found inblood that function as antibodies. IgM is a specific class of antibodies thatseeks out virus particles. In contrast to adults, IgM is the most common type of immunoglobulin in newborn children. It is, therefore, the most useful indicator of the presence of a TORCH infection. The general abnormal, or positive, finding would be high levels of IgM antibody. 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 canmeasure IgM levels in the infant's cerebrospinal fluid, as well as in the blood, if they want to confirm the TORCH results.