β-hCG free (human chorionic gonadotropin free)
Why this test?
- For prenatal screening in the first and second trimester of pregnancy in order to diagnose the risk of developing chromosomal abnormalities of the fetus;
- To diagnose and monitor the course of trophoblast diseases;
- To diagnose the risk of developing and the presence of testicular tumors;
- For the diagnosis of malignant neoplasms that produce hCG;
- To evaluate the effect of specific treatment against tumor neoplasms.
In what cases is it prescribed?
In the first and second trimester of pregnancy;
If trophoblast disease is suspected;
With clinical manifestations and suspicion of malignant processes of the testicles in men;
During a comprehensive examination to detect defects in the development of the fetus.
Human chorionic gonadotropin (hCG) is a glycoprotein hormone with a molecular weight of 37.5 kDa. It consists of two subunits: a nonspecific alpha subunit and a specific beta subunit.
The alpha-subunit of hCG is not unique and is completely identical to the alpha-subunits of luteinizing, follicle-stimulating and thyroid-stimulating hormones of the pituitary gland.
The beta subunit is a sequence of 145 amino acids. It is 80% homologous in structure to the beta chain of luteinizing hormone, but has other biological functions.
Synthesis of hCG is mainly carried out by the syncytial layer of the trophoblast during pregnancy, in low concentrations it is secreted in the pituitary gland. The main amount of circulating hCG is metabolized by liver cells, about 20% is excreted in the urine.
The hormone supports the activity and existence of the corpus luteum, taking over this role from the luteinizing hormone 6-8 days after ovulation.
It is the main hormone of early pregnancy and stimulates the development of the trophoblast. Normally during pregnancy, between the 2nd and 5th week, the amount of beta-hCG doubles every 1.5 days. With multiple pregnancies, it increases proportionally to the number of fetuses. The hCG level reaches its maximum at the 10-11th week, and then gradually decreases.
In addition, hCG stimulates the production of estrogens and weak androgens by ovarian cells and promotes the development of the functional activity of the chorion itself, and later the placenta, which is formed as a result of maturation and growth of chorionic tissue. In men, hCG stimulates the production of testosterone in the testicles.
There are several variants, or isoforms, of hCG, including free beta-hCG, the unbound fraction of the hormone. The determination of this indicator is used in the diagnosis of trophoblastic diseases, some tumors, and pathologies of pregnancy.
An increase in the concentration of free beta-hCG in pregnant women in the first trimester of pregnancy may indicate the presence of a risk of developing trisomy on the 21st chromosome (Down's syndrome) in the fetus. The risk of developing other fetal aneuploidies - conditions in which the body's cells contain an altered number of chromosomes that is not a multiple of the normal haploid set - increases. At the same time, the determination of this indicator is included in the diagnostic screening of chromosomal abnormalities of the fetus in the first and second trimester of pregnancy.
Along with the detection of the free beta-subunit of hCG, it is recommended to determine the level of plasma pregnancy-associated protein-A (PAPP-A) and alpha-fetoprotein (alpha-FP).
A decrease in hormone concentration may indicate the development of other chromosomal abnormalities in the fetus, in particular Edwards syndrome, trisomy on the 18th chromosome.
Determination of the concentration of the beta subunit of hCG is used in the diagnosis and monitoring of the course of trophoblastic diseases in women: cystic fibrosis, choriocarcinoma, trophoblastic tumor in the uterus.An increase in this indicator is noted in breast cancer in women. In men, hormone concentrations can be a sign of testicular tumors, such as testicular teratoma, testicular cancer. Also, an increase in the concentration of the beta-subunit of hCG can be associated with the presence of a tumor process of another localization and accompanied by increased production of hCG.
At the same time, the result of the study of the level of this marker makes it possible to evaluate the effect of chemotherapy treatment on tumor cells.