Sex hormones tests

Encyclopedia of Nursing and Allied Health, 20050229 by Victoria E. DeMoranville

Estriol (E3)

Estriol (E3) is the principal estrogen produced during pregnancy. Estriol is produced by the placenta from dehydroepiandosterone sulfate derived from the fetal liver and adrenals. Estriol levels are low by approximately 25% in Down syndrome and other trisomies. Tests on maternal plasma for alpha-fetoprotein, chorionic gonadotropin, and unconjugated estriol are perfomed at 15-18 weeks gestation. Measurement of unconjugated estriol (uE3) is a better reflection of fetal-derived estriol than is total estriol, and is measured by RIA. Estriol levels are also low for the gestational age in spontaneous abortions and in threatened pregnancy, but are no longer needed for the diagnosis of these conditions.

Progesterone

Progesterone in the nonpregnant female is produced mainly by the ovaries with a small fraction also made by the adrenals. Progesterone levels in plasma are very low prior to ovulation. At ovulation, the level begins to rise due to secretion by the corpus luteum. The progesterone level peaks in the middle of the luteal phase (about one week prior to the next menses). Progesterone causes thickening of the endometrium in order to prepare the ovum for implantation should it be fertilized. In the absence of fertilization, negative feedback of progesterone on the hypothalamus results in suppression of luteinizing hormone and the corpus luteum involutes causing the wall of the uterus to breakdown. If fertilization occurs, the corpus luteum and placenta produce large amounts of progesterone. The most common use of plasma progesterone measurement is to evaluate ovulation. Progesterone is often measured on days 21 and 22 of the menstrual cycle. At this point the progesterone should represent the midluteal peak and levels above 5 ng/L are considered evidence of ovulation. Lower levels indicate a disruption of the normal luteal phase of progesterone production.

Testosterone

In males testosterone is produced by the testes under the control of luteinizing hormone. It is responsible for development of the testes, secondary sexual characteristics, and spermatogenesis. Testosterone is subject to diurnal variation in response to LH and highest plasma levels occur at six to nine AM. Approximately 60% of plasma testosterone is bound to sex hormone binding globulin (SHBG) and almost 40% is bound to albumin. Only about 2% of the hormone is in the free form and is physiologically active. Measurement of free hormone levels is more sensitive than total hormone because small changes in SHBG concentration can increase free hormone levels. A reduction in binding of testosterone to SHBG can be caused by drugs or other steroid hormones, and will increase free hormone levels. In males, plasma testosterone is low in hypogonadism and is measured in male children with delayed or absent sexual maturation. Primary testicular failure may result from Klinefelter syndrome, testicular infection, injury, and other causes. In these cases the plasma testosterone is low, but the LH and FSH are increased. In secondary testicular failure, plasma testosterone, FSH, and LH are decreased. Testosterone levels are also useful for the differential diagnosis of gynecomastia. In addition to low testosterone, gynecomastia can be caused by drugs that interfere with testosterone action, or ectopic tumors that secrete estrogen or chorionic gonadotropin.