The long gestation of the modern home pregnancy test.

The ability of women to confirm their pregnancies in the privacy of their own homes was described as a “private little revolution” 35 years ago, when the early version of the modern home pregnancy test, e.p.t (Warner Chilcott), made its debut in the US (1 ). Indeed, pregnancy tests are among the most widely used home diagnostic tests, having accounted for $228 million in sales in 2012 (http://www.ibisworld.com/industry/ pregnancy-test-kit-manufacturing.html?partnerid prweb). The development of these tests, which are based on the detection of human chorionic gonadotropin (hCG) in the urine, came 50 years after the discovery of hCG by Aschheim and Zondek (2 ) and after several centuries of descriptions of many other pregnancy tests. The first pregnancy test to be recorded was written around 1350 BC in the Berlin medical papyrus: “Barley [and] wheat, let the woman water [them] with her urine every day with dates [and] the sand, in two bags. If they [both] grow, she will bear. If the barley grows, it means a male child. If the wheat grows, it means a female child. If both do not grow, she will not bear at all” (3 ). It is likely that the estrogens (and possibly other growth factors) present in pregnancy urine accounts for the growth stimulation of plants in this and other related plant-based tests described in papyri and later texts. During the Middle Ages, physicians described granules, turbidity, and color changes in urine obtained from pregnant women (3 ). The physicians who diagnosed pregnancy and a host of other medical conditions through examination of the urine were known as “piss prophets,” and they probably arrived at their diagnoses more from being excellent observers of the patient rather than of her urine (Fig. 1). Although others had described a gonadotropic substance present in the placenta, it was Aschheim and Zondek who discovered hCG in the urine in their demonstration of ovarian stimulation of immature female mice injected with the urine of pregnant women (2, 3 ). This first bioassay had an analytical sensitivity of 3000 – 5000 IU/L of urine and took 5 days for a result. Subsequently, numerous other bioassays were described. The end points of these assays were the direct effects of hCG, such as ovulation, ovarian hyperemia, ovarian weight increase, ovarian ascorbic acid depletion, or sperm expulsion (in toads), or the indirect effects of gonadal stimulation, including uterine or ventral prostate increase (3 ). These assays had analytical sensitivities that ranged from 100 IU/L to 18 000 IU/L and required multiple animals for the necessary precision and 2–9 days for a result (3 ). The first immunoassay, a hemagglutination inhibition test, was described in a PhD thesis by Strausser in 1958, but it was never published in the peer-reviewed literature (4 ). The first published report appeared in 1960, when Wide and Gemzell used a passive hemagglutination inhibition technique to measure hCG (4 ). In this assay, hCG was adsorbed to the surface of tannic acid–treated sheep erythrocytes and then mixed with a patient’s urine and anti-hCG antibodies. In the absence of hCG, the antibodies bound to the erythrocytecoated hCG and caused agglutination of the red cells. If hCG was present in the urine, it bound to the antibodies and not to the erythrocytes, and hemagglutination was inhibited. This test was relatively inexpensive and rapid (results in 2 h), could measure 200 IU of hCG per liter of urine, and was marketed in 1962 as Pregnosticon (Organon). Similar principles were used to develop the latex agglutination inhibition tube and slide pregnancy tests. Some of the results were available in 2 min and were sensitive to about 1000 IU/L of urine (3 ). These tests were widely used to diagnose pregnancy in providers’ offices during the 1970s and 1980s. In 1966, Midgley described the first RIA for hCG and its close relative, human luteinizing hormone (hLH) (5 ). This assay required 3 days to run and had an analytical sensitivity of 175 IU/L. A radioreceptor assay that used hLH/hCG receptors from bovine corpora lutea to capture hCG instead of anti-hCG antibodies was developed by Saxena and colleagues (6 ). It required 1 h to perform and was sensitive to 5 IU/L. Neither of these assays could discriminate between hCG and hLH; therefore, to measure hCG specifically in pregnancy serum or urine samples required setting the detection limit at a value above the highest physiological hLH concentration that could be seen during the midcycle spike in ovulating women or above the con1 Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA. * Address correspondence to the author at: Department of Medicine, Rm. B118, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Los Angeles, CA 90048. Fax 310-423-0437; e-mail [email protected]. Received April 22, 2013; accepted July 18, 2013. Previously published online at DOI: 10.1373/clinchem.2013.202655 2 Nonstandard abbreviations: hCG, human chorionic gonadotropin; hLH, human luteinizing hormone. Clinical Chemistry 60:1 18–21 (2014) Reflection