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Pregnancy symptoms but negative test11/13/2023 UPTs are a qualitative, two-site sandwich immunoassay that works by binding β-hCG molecules in the urine. On the other hand, hCG-βcf is highest in mid-pregnancy urine. For example, H-hCG is the predominant form of β-hCG produced after implantation but accounts for less than 5% of β-hCG in the second and third trimesters. The relative concentrations of each different form change throughout the course of pregnancy. These include hyperglycosylated hCG (H-hCG), nicked hCG, free β-subunit, the core fragment of β-hCG (hCG-βcf), and others. To further complicate matters, the β-subunit exists in several different forms. Therefore, UPTs specifically detect the β-subunit of hCG, or β-hCG. These hormones could potentially have cross-reactivity with the α-subunit of hCG. The α-subunit of hCG is identical to the α-subunit of other hormones in the glycoprotein family, including luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). hCG is a glycoprotein composed of α- and β-subunits. Human chorionic gonadotropin (hCG) is produced almost exclusively by the trophoblast, more specifically by the cytotrophoblast and syncytiotrophoblast, of the placenta once implantation has occurred. Occasionally, UPTs produce false results, which can alter the management of the patient in question and may lead to delays in diagnosis. ![]() Understanding the mechanism by which UPTs produce their results is important to understanding the accuracy and reliability of this testing modality. UPTs are widely available, reliable, relatively inexpensive, and offer quick results. Urine pregnancy tests (UPTs) are used to detect the presence of human chorionic gonadotropin (hCG) in the urine and, when positive, are highly suggestive of pregnancy. It is important for physicians to understand and recognize the limitations of the urine pregnancy test in order to best facilitate care for patients who may have a false-negative pregnancy test result, as there are significant risks of improper patient management with a multiple gestation pregnancy or gestational trophoblastic disease. The patient ultimately delivered triplets by repeated caesarean section. Additional workup revealed significantly elevated serum quantitative β-hCG and bedside ultrasound revealed multiple gestation intrauterine pregnancy. Repeat testing resulted in a negative urine pregnancy test. Here, we present a case of a patient with a prior positive urine pregnancy test who presents with symptoms consistent with early pregnancy. Less commonly known is that the test may provide a false-negative result when urinary β-hCG concentrations are extremely elevated, such as gestational trophoblastic disease or multiple gestations. Although a nearly perfect test, it is common knowledge that this test can be falsely negative if performed too early in the pregnancy when urinary β-hCG concentrations fall below detectable levels. ![]() This test relies on the detection of β-human chorionic gonadotropin (β-hCG) molecules in the urine through a two-site sandwich immunoassay. Urine pregnancy tests (UPTs) are a highly reliable method of detecting pregnancy, with reported 100% sensitivity and 99.2% specificity.
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