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Prim Care. 1986 Dec;13(4):667-77.

Update on pregnancy testing.

Abstract

Laboratory testing is an extension of the physical examination, reaching sites that are otherwise inaccessible to the examiner. Pregnancy testing is one such diagnostic extension. Like physical examination, it must be used carefully. In choosing a pregnancy test for office use, many factors must be considered, so that accurate information will be available for patient management. Such factors as the technical skills and training of the office staff performing the test, shelf life of the test, need to refrigerate reagents, and frequency of usage are all important considerations. Test results must always be correlated with specific patients and clinical findings, and at times, doubts may be allayed by simply retesting patients with negative or equivocal results at a later time (currently a matter of days instead of weeks). Recent developments in pregnancy testing have been directed toward improved sensitivity and specificity, as well as speed, simplicity, and reduced cost. The clinical issue of greatest interest to most primary care physicians is the early diagnosis of normal pregnancy, where "early" may be defined as prior to the first missed menses. Diagnosis in the first 21 days of gestation is currently possible with more sensitive methods, and especially with enzyme-linked immunoassay. In this regard, because of its easy methodology and basic reliability, the enzyme-linked immunoassay may well become the new standard for office pregnancy testing.

PIP:

Pregnancy tests aimed at detecting the presence of human chorionic gonadotropin (hCG) in maternal plasma and its excretion in urine have become a valuable diagnostic tool. The newer tests offer greater sensitivity and specificity than the older 2-minute slide tests or tube tests. At present, the most promising pregnancy tests are the enzyme-linked immunoassays. These are qualitative tests that involve enzyme-linked immunosorbent assay (ELISA) and monoclonal antibodies. This technology is readily adaptable to most clinic and office settings and may be run on either serum or urine specimens. Advantages include its ready availability, simplicity, sensitivity, and specificity for the beta subunit of hCG. Over-the-counter pregnancy tests for use by nonprofessionals have been available since the mid-1970s; however, these tests have a relatively high (25%) false-negative rate. Among the problems that have arisen in testing for pregnancy by hCG determination are the interference of proteinuria with urine pregnancy tests, an irreducible level of technical error, the tendency of certain drugs to produce a false-positive result, and quality control. In general, physicians should consider several factors--the technical skills and training of the office staff performing the tests, shelf life of the test, the need to refrigerate reagents, and frequency of usage--in selecting a pregnancy test for office use. Test results should be correlated with specific patients and clinical findings, and patients with negative or equivocal results should be retested a few days later.

PMID:
3541014
[Indexed for MEDLINE]

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