Human Chorionic Gonadotropin (hCG)Dec 05, Author: It can support pregnancy by allowing for the production of progesterone, which can help to prepare the lining of the uterus for implantation. It ,ales of cells that ultimately form the placenta, which provides nutrition to the egg after it has been fertilized and connects to the uterine wall. The alpha and beta-subunits have separate genes on separate chromosomes chromosomes 6 and 19, respectively. After synthesis, the alpha heta beta-subunits are bonded with a noncovalent bond before being released beta hcg in males the circulation.
Human Chorionic Gonadotropin (hCG): Reference Range, Interpretation, Collection and Panels
Dec 05, Author: It can support pregnancy by allowing for the production of progesterone, which can help to prepare the lining of the uterus for implantation. It consists of cells that ultimately form the placenta, which provides nutrition to the egg after it has been fertilized and connects to the uterine wall.
The alpha and beta-subunits have separate genes on separate chromosomes chromosomes 6 and 19, respectively. After synthesis, the alpha and beta-subunits are bonded with a noncovalent bond before being released into the circulation. Clearance half-life is approximately days.
Therefore, by 3 months of age, levels comparable to adults should be reached. A rise in hCG levels above the reference range in patients with a history of an hCG-producing condition is suggestive of recurrent disease.
Open Table in a new window. Human chorionic gonadotropin hCG is a dimer consisting of a amino acid beta-subunit that is unique to hCG and a 92 amino acid alpha-subunit. The alpha-subunit contains 2 N-linked oligosaccharides; the beta-subunit contains 2 N-linked oligosaccharides, as well as 4 O-linked oligosaccharides on the C-terminal extension.
Gestational and nongestational trophoblasts are by far the most common sources of hCG, but a small amount of the hormone may also be produced by the pituitary gland and nontrophoblastic malignancies. The syncytiotrophoblast covers the villous tree and has several functions, such as transport of gases, nutrients, and waste products and synthesis of peptide and steroid hormones that regulate placental, fetal, and maternal systems.
The syncytiotrophoblast produces regular hCG, which promotes progesterone production by the corpus luteum until placental progesterone production becomes established after 6 weeks of gestation.
Regular hCG also appears to play a role in myometrial spiral artery angiogenesis. The level of free beta-subunit of hCG is often determined in pregnant women as part of maternal serum screening for Down syndrome. The free beta-subunit variants measured depend on the assay. Increased total hCG levels in the first and second trimester are associated with Down syndrome, while decreased levels may occur in trisomy Elevations of hCG can also occur in multiple pregnancies, singleton pregnancies in which the gestational age has been overestimated, triploidy, fetal loss, and hydrops fetalis.
HCG promotes trophoblast growth and invasion. Partial moles produce less regular hCG than complete moles. In gestational trophoblastic neoplasias, such as invasive mole and choriocarcinoma, a high level of hCG can help to distinguish invasive from noninvasive mole, although some overlap occurs in their normal ranges.
Serial measurement of hCG levels is standard follow-up of women diagnosed with complete or partial mole. An increasing or plateauing level of total hCG is diagnostic of invasive disease invasive mole or choriocarcinoma. Choriocarcinoma consists of sheets of anaplastic cytotrophoblasts and syncytiotrophoblasts without chorionic villi. Some intermediate trophoblasts may also be seen. The level of hCG correlates with tumor mass. The normal pituitary gland produces a small amount of hCG.
Pituitary production of hCG is most notable around the time of menopause natural or surgical and prior to ovulation, which are times when LH levels peak. One possible explanation is that a small amount of hCG is produced along LH because the single LH beta-subunit gene is buried among the 7 back-to-back hCG beta-subunit genes.
Return of the serum hCG concentration to undetectable following pregnancy termination varies widely from days. The period of time depends primarily upon the hCG concentration at the time of termination. The hCG concentration peaks at weeks at approximately 90, mIU. This is in contrast with term pregnancy, for which the hCG concentration is lower.
The decline in serum hCG is rapid for the first several days half-life hours and then proceeds more slowly half-life hours. Outside of pregnancy, hCG may be secreted by abnormal germ cell, placental, or embryonal tissues, in particular seminomatous and nonseminomatous testicular tumors; ovarian germ cell tumors; gestational trophoblastic disease GTD, hydatidiform mole, and choriocarcinoma ; and benign or malignant nontesticular teratomas.
Rarely, other tumors including hepatic, neuroendocrine, breast, ovarian, pancreatic, cervical, and gastric cancers may secrete hCG, usually in relatively modest quantities.
During pathologic hCG production, the highly coordinated secretion of alpha and beta subunits of hCG may be disturbed. In addition to secreting intact hCG, tumors may produce disproportionate quantities of free alpha subunits or, more commonly, free beta subunits. Assays that detect both intact hCG and free beta hCG, including this assay, therefore, tend to be more sensitive in detecting hCG-producing tumors.
With successful treatment of hCG-producing tumors, hCG levels should fall, with a half-life of hours, and eventually return to within normal limits. An elevated HCG level may be physiologic, pathophysiologic from a tumor or artifactual from a false-positive hCG test. Unless a tumor is evident, excluding these possibilities before initiating chemotherapy for assumed persistence of disease is essential.
A false-positive HCG test may be caused by naturally occurring cross-reacting antibodies that interfere with the test. The capture and tracer antibodies used for hCG testing may be goat, sheep, or rabbit polyclonal antibodies or mouse, goat, or sheep monoclonal antibodies. Humans extensively exposed to animals or certain animal byproducts can develop human antibodies against these animal antibodies HAAA. In addition, humans naturally generate human anti-human immunoglobulin antibodies that can cross-react with and bind animal antibodies; these are called heterophilic antibodies.
Also, recent infections or exposure to mononucleosis can produce these HAAAs; those with IgA deficiency syndrome also often have heterophilic antibodies. The false positive HCG test can lead to the misdiagnosis of cancer and sometimes lead to needless surgery and chemotherapy. To prevent false testing, animal serum and nonspecific animal antibodies are added to HCG assays with capture antibody, tracer antibody, and other components.
This excess of nonspecific antibodies overwhelming saturates heterophilic antibodies and HAAA in human serum samples and usually eliminates their interference with the assay.
This method does not always work, however, and false positive cases still occur. This understandably creates confusion, as some false positive cases are incorrectly interpreted as recurrence of gestational trophoblastic disease. Patients who have false-positive hCG test results are also at risk for other false positives, such as CA and thyroid antibodies. They should make their future health care providers aware of this problem and it should be noted in their medical records.
First-trimester screening biochemical markers free beta-subunit human chorionic gonadotropin, pregnancy-associated plasma protein-A and risk of early fetal loss.
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Reference Range Human chorionic gonadotropin hCG is produced during pregnancy.