Because immunoglobulin M (IgM) is usually produced in significant quantities during the first exposure of a patient to an infectious agent, the detection of specific IgM can be of diagnostic significance. This immunologic characteristic is particularly important in diseases that do not manifest decisive clinical signs and symptoms (e.g., toxoplasmosis) or under conditions in which a rapid therapeutic decision may be required (e.g., rubella).

Antibody Significance

In many diseases, infected individuals show a spectrum of responses. Some patients may develop and manifest antibodies from a subclinical infection or after colonization of an agent without actually developing disease. In these patients, the presence of antibody in a single serum specimen or a comparative titer of antibody in paired specimens may merely indicate past contact with the agent; the presence of antibodies cannot be used for the accurate diagnosis of a recent disease. In comparison, some patients may respond to an antigenic stimulus by producing antibodies that can cross-react with other antigens. These antibodies are nonspecific and may lead to misinterpretation of serologic tests.

Serologic diagnosis of recent infection using acute and convalescent specimens is the method of choice. Except for the detection of IgM or in diseases with no chance of developing an immune response (e.g., rabies virus, botulism toxin), testing a single specimen is usually not recommended. In a number of circumstances, when only one specimen is tested to determine immune status, antibody to past infection or to immunization can be determined.

The testing protocols described in this chapter for the immunologic detection of representative infectious diseases are examples of the types of procedures typically encountered in the immunology-serology laboratory.

TORCH Testing

 Procedures that specifically evaluate the presence of IgM or IgG are frequently used to detect CMV, herpesviruses (types 1 and 2), Toxoplasma gondii, and rubella. The names of the tests have been grouped under the acronym TORCH: Toxoplasma, other (viruses), rubella, CMV, and herpes (Tables 1 and 2).

Table1. TORCH Antibodies: Immunoglobulin M

Table2. TORCH Antibodies: Immunoglobulin G

A spectrum of congenital defects called TORCH syndrome occurs with maternal exposure to rubella (also to T. gondii, CMV, and HSV). Congenital defects may be asymptomatic. A TORCH panel 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. Women infected with Toxoplasma or CMV may have flulike symptoms that are not easily differentiated from other illnesses. Antibody testing will help diagnose an infection that may be harmful to the fetus.

In addition, a TORCH panel may be ordered on the new born if the infant shows any signs suggestive of these infections, such as exceptionally small size relative to gestational age, deafness, mental impairment, seizures, heart defects, cataracts, enlarged liver or spleen, low platelet level, and/or jaundice.

Toxoplasmosis

Toxoplasmosis infection during pregnancy can cause congenital infection and manifestations, such as mental retardation and blindness. Hydrocephalus, intracranial calcification, and retinochoroiditis are the most common manifestations of tis sue damage from congenital toxoplasmosis.

A neonatal screening program based on detecting IgM antibodies against T. gondii alone would identify 70% to 80% of congenital toxoplasmosis cases. The prevalence of congenital toxoplasmosis is 1/10,000 live births in the United States, in which 85% of women of childbearing age are susceptible to acute infection with T. gondii.

Cytomegalovirus

Cytomegalovirus is the most common congenital virus infection in the world. Both primary and recurrent infection can result in fetal infection. The birth prevalence of congenital CMV infection varies from 0.3% to 2.4% and at least 90% of congenitally infected infants have no clinical signs. CMV causes illnesses ranging from no clinical signs to prematurity, encephalitis, deafness, hematologic disorders, and death.

Congenital CMV infection is described in 30,000 to 40,000 newborns each year in the United States; approximately 9000 of these children have permanent neurologic sequelae. The death rate from symptomatic congenital CMV infection is approximately 30%.

Rubella

Rubella virus infection during early pregnancy can lead to severe birth defects known as congenital rubella syndrome. Sequelae of rubella virus infection include three distinct neurologic syndromes:

 • Postinfectious encephalitis after acute infection

 • Neurologic manifestations after congenital infection

• Rare neurodegenerative disorder, progressive rubella panencephalitis, that can follow congenital or postnatal infection

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مواضيع ذات صلة

progesterone receptor assay (PR assay, PRA, PgR)

progesterone assay

pregnancy-associated plasma protein-A (PAPP-A)

HPV DNA Detection

platelet volume, mean (Mean platelet volume [MPV])

platelet count (Thrombocyte count)

platelet antibody detection (Antiplatelet antibody detection)

Future Directions of Molecular Diagnostic Testing

Next Generation Sequencing Technology

Analysis of Amplification Products

platelet aggregation test (Ristocetin test)

plasminogen activator inhibitor 1 (PAI-1)