Luteinizing Hormone (LH), 05 Specimens

Overview:

The primary use of LH measuremnt is in evaluating the normalcy of hypothalamic-pituitary-gonadal axis. Measurementof serum gonadotropin levels will allow for distinguishing between primary gonadal failure and deficient gonadal stimulation. LH measurement may also be of clinical importance because growth hormone and LH are frequently the first hormones to be affected by pituitary disease. The serum analysis of LH has also been found to be very useful in the diagnosis and treatment of infertility of women. LH (luteinizing hormone), together with FSH (follicle stimulating hormone), belongs to the gonadotropin family. LH and FSH regulate and stimulate the growth and function ofthe gonads (ovaries and testes) synergistically.[2-4] Like FSH, TSH and hCG, LH is a glycoprotein consisting of two subunits (alpha- and beta-chains). This proteohormone, whichconsists of 121 amino acids[3] and three sugar chains, has a molecular weight of 29500 daltons[4]. In women, the gonadotropins act within the hypothalamus- pituitary-ovary regulating circuit to control the menstrual cycle[5,6]. LH and FSH are released in pulses from the gonadotropic cells of the anterior pituitary and pass via the bloodstream to the ovaries. Here the gonadotropins stimulate the growth and maturation of the follicle and hence the biosynthesis of estrogens and progesterones. The highest LH-concentrations occur during the mid-cycle peak and induce ovulation and formation of the corpus luteum, theprincipal secretion product of which is progesterone. Determination of the LH concentration is used in the elucidation of dysfunctions within the hypothalamus- pituitary-gonads system. In the Leydig cells of the testes, LH stimulates the production of testosterone. The determination of LH in conjuction with FSH is utilized for the following indications: congenital diseases with chromosome aberrations (e.g. Turner's syndrome), polycystic ovaries (PCO), clarifying the causes of amenorrhea, menopausal syndrome, and suspected Leydig cell insufficiency2,5,6].

Secretion of both LH and FSH are pulsatile, in response to the normal intermittent release of gonadotropin releasing hormone (GnRH). In addition, in females both FSH and LH varyover the course of the menstrual cycle, with peaks at time of ovulation. Thus, interpretation of a single determinationmay be difficult. It has been suggested that samples be obtained at 15 to 30 minutes intervals and equal volumes of serum be pooled to decrease the effect of pulsatile secretion. As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes[1].In rare cases, interference due to extremely high titers of antibodies to streptavidin and ruthenium can occur[1]. The test contains additives, which minimize these effects.