The search for an effective and reliable pregnancy test began as early as the 1920s. The first home pregnancy test, E.P.T. (Warner–Lambert), was approved by the Food and Drug Administration (FDA) in 1976 and marketed to the public in 1977. Since then, millions of women have used these devices for early detection of pregnancy. Early detection allows the patient to make lifestyle changes and to seek prenatal care.
Home pregnancy tests (HPTs) are designed to detect HCG in the urine. Trophoblasts of the fertilized ovum begin to produce HCG after implantation until the placenta develops and begins producing HCG on its own. HCG is usually detectable 10–12 days after fertilization, but in some women detection may take up to three weeks. HCG peaks 60–70 days after fertilization and then plateaus as pregnancy progresses. HPTs produced after 1990 involve immunometric assays that use monoclonal or polyclonal antibodies to bind to HCG and produce a reaction resulting in a color change, the appearance of lines, or, with the new digital models, the appearance of the word "pregnant."[36,37]
In April 2007 there were 162 pregnancy test products registered with FDA, of which 33 were intended for home use ( Table 2 ).[38,39,40,41] Patients often seek guidance about the "best test," and pharmacists can assist patients by knowing the limitations of HPTs. Most HPTs claim to be 94–99% accurate, but these claims are based on testing under ideal conditions by the manufacturers. Studies have shown that, when patients use HPTs in the home environment, accuracy and effectiveness may decrease. A meta-analysis of five studies involving a total of 16 HPTs found that summary sensitivity scores decreased from 0.91 (95% confidence interval [CI], 0.84–0.96) to 0.75 (95% CI, 0.64–0.85) and that effectiveness scores (comparison of the relative and absolute ability of an HPT to distinguish between women who are pregnant and those who are not) decreased from 2.75 (95% CI, 2.3–3.2) to 0.82 (95% CI, 0.4–1.2) when HPTs were used by woman volunteers at home versus in the laboratory setting. The wide variation in HCG concentrations (e.g., from 12 to 2438 IU/L during the fourth week of pregnancy) is another limiting factor of HPTs. The two major factors that reduced sensitivity and effectiveness scores in the volunteer groups were user error and testing too early (before HCG was detectable).
Several studies show that most HPTs work best when the HCG concentration reaches a minimum of 25 IU/L.[39,40] However, this concentration is rarely achieved on the day or week of missed menstruation, which is when most patients desire to self-test.[39,40,43] Complicating the situation are the multiple forms of HCG: hyperglycosylated HCG, intact HCG, free α-subunit, and free β-subunit. Hyperglycosylated HCG is the primary form detected in early pregnancy (80% of HCG one week after implantation), whereas the intact form is more prevalent in the second and third trimesters. Curiously, not all HPTs are designed to effectively detect hyperglycosylated HCG. A 2001 study in which 15 HPT products were tested with 592 urine samples found that only 7 devices effectively detected the hyperglycosylated form.
To add even more to the confusion, the literature is inconsistent in documenting problems with HPTs. In 1996, Consumer Reports recommended Answer (Armkel) as the top HPT on the market. In 2003, based on new testing, Consumer Reports chose First Response Early Results (Armkel) and Clear Choice (Pharmatech) as the top HPTs. The First Response Early Results HPT also performed well in a study by Cole et al. However, the Clear Choice and Confirm (Durex) products had significant technical problems: Both gave positive results for urine containing zero HCG. A 2006 survey of 5000 community pharmacists showed E.P.T. and First Response Early Results to be the two most recommended tests. Overall, First Response Early Results may be the best test for detecting pregnancy before the fourth week of gestation, when HCG levels are low. After that point, most of the HPTs are equivalent.
The following information should be obtained from the patient to help decide if an HPT is appropriate: number of days after unprotected sex, number of days since missed menstrual period; experience with HPTs, preferred urine-collection method, patient limitations (visual impairment, colorblindness, tremors, illiteracy, etc.), and presence of interactions involving any drug (e.g., HCG injection) or condition (e.g., HCG-secreting tumors, ovarian cysts, miscarriage or abortion in the preceding eight weeks).[36,37] Patients should understand that HCG levels are extremely variable from the day of missed menstruation to the fourth week of gestation, that there is a chance for false-negatives, and that retesting is necessary if menstruation has not begun within one week of a negative finding. If the repeat test is negative and menstruation does not begin as expected, patients should see a physician for a serum HCG test and a physical examination. Patients should be aware that early pregnancy losses, which are estimated to occur in 30% of patients, may result in a positive early test result but negative follow-up test results. Patients may benefit from tips for increasing the sensitivity of the test, such as waiting 10 minutes before reading results, sampling the first urine of the day, and making sure that the test strips are stored properly and have not expired.
Am J Health Syst Pharm. 2008;65(4):299-314. © 2008 American Society of Health-System Pharmacists
Cite this: Devices for Home Evaluation of Women's Health Concerns - Medscape - Feb 15, 2008.