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Human Chorionic Gonadotropin (hCG) and Testing

by len king on Apr 25, 2023

Human Chorionic Gonadotropin (hCG) and Testing

Human chorionic gonadotropin (hCG) is a glycoprotein hormone that is secreted from the placenta and is structurally similar to the pituitary hormones FSH, TSH and LH. Its α subunit (molecular weight 15,000-20,000 daltons) is identical to these hormones, but the β subunit is different and exhibits different immunological and biological activities. the polypeptide sequence of the β subunit (molecular weight 25,000-30,000 daltons) has some similarities to the β chain of LH, but the region at the end of the carboxyl terminus is unique to it. Shortly after the fertilized egg enters the uterus and lays, the trophoblast begins to secrete hCG . This hormone keeps the corpus luteum releasing steroid hormones until the placenta can release steroid hormones. In a normal pregnancy, the serum hCG concentration generally reaches 50 mIU/ml (IU/l) one week after the fertilized egg is laid, and doubles every 1.5 to 3 days for 6 weeks. During the first trimester, hCG levels continue to rise and then slowly decline until the end of pregnancy, after delivery, hCG levels return to < 5 mIU/ml (IU/l), usually reaching unmeasurably low values after a few days. This hormone is an excellent marker of pregnancy and hCG in serum is usually < 5 mIU/ml (IU/l) in healthy and non-pregnant individuals. During pregnancy, hCG concentrations change as described above, with abnormal low values or early large decreases suggesting abnormal conditions such as ectopic pregnancy or preterm abortion.
The original biological methods for determining hCG by measuring the response of gonadal organs in different animals were poorly sensitive, difficult to perform, and required a large number of samples. The traditional method for detecting hCG in urine was the latex agglutination or agglutination inhibition assay, but with the development of science and technology, in 1972, Vaitukaitis et al. developed the technique of radioimmunoassay for hCG, which made it possible to detect hCG more sensitively and rapidly. The subsequent establishment of two-site immunoradiometric assays made the assay more sensitive, specific and accurate.
Clinical significance
The examination of HCG is important for the diagnosis of early pregnancy and is valuable for the diagnosis, differentiation and observation of the course of pregnancy-related diseases, trophoblastic tumors and other diseases.
1) Diagnosis of early pregnancy: HCG can rise to more than 2500 IU/L at 35-50 days after conception. 80,000 IU/L at 60-70 days, and urinary HCG is often higher in multiple pregnancies than in one pregnancy. 2) Determination of abnormal pregnancy and placental function:
① Ectopic pregnancy: If ectopic pregnancy, this test has only 60% positive rate. HCG can still be positive after 3 days of uterine bleeding, so HCG test can be used as a differentiation between it and other acute abdominal diseases. HCG is often 312-625 IU/L.
② Miscarriage diagnosis and treatment: HCG test can still be positive in incomplete miscarriage if there is still placental tissue remaining in the uterus; HCG turns from positive to negative in complete miscarriage or stillbirth, so it can be used as a reference basis for fetal preservation or aspiration treatment.
③ Pre-eclampsia abortion: If the HCG in urine remains high, inevitable abortion will not occur. If the HCG is below 2500 IU/L and decreases gradually, there is a possibility of miscarriage or stillbirth, and when it decreases to 600 IU/L, inevitable miscarriage will occur. If the HCG continues to fall during the treatment of fetal preservation, it means that the fetal preservation is ineffective, if the HCG keeps rising, it means that the fetal preservation is successful.
④ Serum HCG should be below 1000 IU/L at 4 days after delivery or 13 days after abortion, and normalize at 9 days after delivery or 25 days after abortion. If this situation is not met, the possibility of abnormality should be considered.
3. Trophoblastic tumor diagnosis and treatment monitoring
① Staphyloma, malignant staphyloma, chorioepithelial carcinoma and testicular teratoma have significantly elevated HCG in urine, right up to 100,000 to millions of IU/L. It can be diagnosed by dilution test such as 1:500 dilution urine positive before 12 weeks of gestation and 1:250 dilution urine positive after 12 weeks of gestation, which is valuable for the diagnosis of staphyloma. 1:100 to 1:500 dilution urine positive for Choriocarcinoma also has diagnostic value. If HCG in urine is elevated in men, testicular tumors such as spermatogonial cell carcinoma, malformations and ectopic HCG tumors should be considered.
② Patients with trophoblastic tumors should have urinary HCG <50 IU/L after 3 weeks postoperatively and negative in 8-12 weeks; if HCG does not decrease or does not turn negative, it suggests that there may be residual lesions, and such cases are often prone to recurrence, so regular examination is needed.

4. Other menopause, ovulation and bilateral oophorectomy can lead to elevated luteinizing hormone, and a positive pregnancy test with anti-HCG antibodies due to the same composition of the alpha peptide chain of LH and HCG, which can be identified by a monoclonal two-point enzyme immunoassay of β-HCG. HCG can also be increased in endocrine diseases such as pituitary disease, hyperthyroidism, gynecological diseases such as ovarian cysts and uterine cancer.

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