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  • Title: Current status of pregnancy testing.
    Author: Sheehan C.
    Journal: Am J Med Technol; 1983 Jul; 49(7):485-8. PubMed ID: 6353918.
    Abstract:
    Attention in this discussion of the current status of pregnancy testing is directed to the following: the history of the early methods; current testing of the human chorionic gonadotropin (HCG), and newer assay developments. The development of laboratory assays for the detection of pregnancy began over 50 years ago with the report of Aschheim and Zondek. The test was performed by injecting urine into infantile mice, sacrificing the mice after 100 hours, and performing a macroscopic and microscopic examination of the ovaries for the formation of corpora lutea or hemorrhages in the ovary. Other bioassays were developed to minimize the disadvantages of the Aschheim-Zondek test. The bioassays are plagued with problems such as urine toxicity; care, handling, and expense of animals maintenance; and animal variability in sensitivity to the hormone. The in vitro, immunologic assays have changed as the hormone has been characterized. Human chorionic gonadotropin is a glycoprotein hormone produced and secreted by the trophoblast and later by the chorion and placenta in pregnant women. HCG consists of 2 noncovalently linked polypeptide chains designated as the alpha and beta subunits. Current testing includes the following methodologies: direct hemagglutination, hemagglutination inhibition, latex agglutination inhibition, radioimmunoassay, radioreceptor assay, and enzyme immunoassay. The agglutination reactions were developed in the 1950s and 1960s. As in any agglutination reaction, there must be a soluble reactant and the other reactant fixed to or part of an insoluble particle. The hemagglutination and latex agglutination inhibition assays differ from the direct agglutination method in that sufficient urine or serum HCG will neutralize the soluble antibody reagent. The application of radioimmunoassay (RIA) to the detection of HCG occurred during the 1970s. The 1980s ushered in the next generation of pregnancy testing, enzyme immunoassay (EIA). The qualitative detection of HCG in serum or urine using EIA is reported to be as sensitive as RIA. Given the specificity of the beta subunit HCG RIA protocols and the confirmation of biologic activity of the HCG by radioreceptor assay (RRA), the question is what further approaches have been undertaken. Under investigation are: faster results with the same specificity, use of nonradioactive labels, and use of monoclonal antibodies. Fast results with better specificity have been produced by incorporating heterologous antiserum directed against the beta subunit of HCG into slide and tube agglutination assays. Preference for EIA over RIA methods is based on the advantages of greater shelf life, lack of radioactive hazard, and of need for specialized disposal.
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