Human Chorionic Gonadotropin (hCG), Quantitative, Pregnancy, Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Human chorionic gonadotropin (hCG) is a glycoprotein hormone that consists of 2 subunits (alpha and beta chains), which are associated to comprise the intact hormone. The alpha subunit is similar to those of luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone. The beta subunit of hCG differs from other pituitary glycoprotein hormones, which results in its unique biochemical and immunological properties. This method quantitates the sum of intact hCG plus the beta subunit.
hCG is produced in the placenta during pregnancy. In nonpregnant women, it can also be produced by tumors of the trophoblast, germ cell tumors with trophoblastic components, and some nontrophoblastic tumors. The biological action of hCG serves to maintain the corpus luteum during pregnancy. It also influences steroid production. The serum in pregnant women contains mainly intact hCG. Measurement of the hCG concentration permits the diagnosis of pregnancy as early as 1 week after conception.
Early detection of pregnancy
Investigation of suspected ectopic pregnancy or other pregnancy-related complications
Monitoring in vitro fertilization patients
Values between 5 and 25 IU/L are indeterminate for pregnancy. Consider confirming with repeat test in 72 hours. Values in pregnancy should double every 3 days for the first 6 weeks.
Elevated concentrations of human chorionic gonadotropin (hCG) measured in the first trimester of pregnancy are observed in normal pregnancy, but may serve as an indication of chorionic carcinoma, hydatiform mole, or multiple pregnancy.
Decreasing hCG concentrations indicate threatened or missed abortion, recent termination of pregnancy, ectopic pregnancy, gestosis or intrauterine death.
Both normal and ectopic pregnancies generally yield positive results of pregnancy tests. The comparison of quantitative hCG measurements with the results of transvaginal ultrasonography (TVUS) may aid in the diagnosis of ectopic pregnancy. When an embryo is first large enough for the gestation sac to be visible on TVUS, the patient generally will have hCG concentrations between 1,000 and 2,000 IU/L. (These are literature values. Definitive values for this method have not been established at this time.) If the hCG value is this high and no sac is visible in the uterus, ectopic pregnancy is suggested. Elevated values will also be seen with choriocarcinoma and hydatiform mole.
Peri- and postmenopausal females may have detectable hCG concentrations (<14 IU/L) due to pituitary production of hCG. Serum follicle stimulating hormone measurement may aid in ruling out pregnancy in this population. Cutoffs of >20 to 45 IU/L have been suggested and are method dependent.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
False-elevations (called phantom human chorionic gonadotropin: hCG) may occur with patients who have human antianimal or heterophilic antibodies.
Some specimens may not dilute linearly due to abnormal forms of hCG.
Elevated hCG concentrations not associated with pregnancy are found in patients with other diseases such as tumors of the germ cells, ovaries, bladder, pancreas, stomach, lungs, and liver. This test is not intended to detect or monitor tumors or gestational trophoblastic disease.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative: <5 IU/L
Indeterminate: 5-25 IU/L
Positive: >25 IU/L
Suggest repeat testing of indeterminate results in 72 hours.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
Snyder JA, Haymond S, Parvin CA, et al: Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem 2005;51:1830-1835