BETA-HUMAN CHORIONIC GONADOTROPHIN (bhCG)

CLINICAL UTILITY:

Pregnancy: Human chorionic gonadotropin (hCG) is a glycoprotein hormone, produced by the placenta, with structural similarity to the pituitary hormones FSH, TSH, and LH. The alpha subunit (MW 15,000–20,000 daltons) is common to all of these hormones but the beta subunits differ, and confer immunological and biological specificity. Beta hCG (MW 25,000–30,000 daltons) shares several peptide sequences with beta LH, but has a unique carboxyl terminal region.

Shortly after implantation of a fertilized ovum into the uterine wall, the trophoblast begins to produce hCG. The hormone maintains steroid secretions of the corpus luteum until the placenta can do so. During a normal pregnancy, serum hCG is generally approximately 50 mIU/ml (IU/l) in the week after conception, and doubles every 1.5–3 days for the first six weeks. Levels continue to rise until the end of the first trimester, then gradually fall to a lower level for the remainder of the pregnancy. After delivery, hCG returns to < 5 mIU/ml (IU/l) and is usually undetectable several days postpartum.

The hormone is an excellent marker for pregnancy. Healthy, non-pregnant individuals have low [< 5 mIU/ml (IU/l)] to undetectable hCG in serum. During pregnancy, hCG concentrations increase as noted above and then show a gradual decrease after the first trimester. Unusually low or rapidly declining levels may indicate an abnormal condition such as an ectopic pregnancy or impending spontaneous abortion.

Tumor Markers:
Clinical applications for the hCG beta assay as a tumor marker include the diagnosis and management of hydatidiform mole and choriocarcinoma. The hCG beta assay is a valuable tool also in the diagnosis, staging and management of patients with testicular and ovarian germ-cell tumors. Ectopic production of hCG beta has been reported in cases such as carcinoma of the stomach, liver, pancreas, breast and in multiple myeloma and melanoma.

Prenatal Risk Panels:
bhCG results are used as one factor in a multivariant analysis to calculate the prenatal risk for Down syndrome and Trisomy 18. All risk calculations are done using the AFP Expert program. Questions regarding interpretation of maternal screens and amniotic fluid results and possible further testing should be referred to Genetic Counselors, University of Washington Medical Center. Phone number (206) 593-3753.

METHOD DESCRIPTION:

Total beta-hCG assay is a two-site immunoenzymatic (“sandwich”) immunoassay.

REFERENCE RANGE:

Non-maternal (Tumor marker) samples: 0-5 mIU/ml Maternal serum bhCG results do not have a reference range.

SPECIMEN REQUIREMENTS:

Serum (2.0 ml - min volume 0.8 ml) is the recommended sample type.