Luteinizing Hormone (LH) – Function and Clinical Importance
Luteinizing hormone (LH) is a gonadotropin produced by the pituitary gland that regulates ovulation, the menstrual cycle, and testosterone production.
Things worth knowing about "Luteinizing Hormone"
Luteinizing hormone (LH) is a gonadotropin produced by the pituitary gland that regulates ovulation, the menstrual cycle, and testosterone production.
What is Luteinizing Hormone?
Luteinizing hormone (LH) is a glycoprotein hormone produced and secreted by the anterior pituitary gland. It belongs to the group of gonadotropins and plays a central role in regulating reproductive function in both women and men. The release of LH is controlled by gonadotropin-releasing hormone (GnRH), which is secreted by the hypothalamus.
Mechanism of Action
LH binds to specific receptors located in the gonads – the ovaries in women and the testes in men – triggering different physiological responses in each sex.
Effects in Women
- LH works together with follicle-stimulating hormone (FSH) to stimulate the growth and maturation of ovarian follicles.
- A sudden, sharp rise in LH levels – known as the LH surge – triggers ovulation, the release of a mature egg from the ovary.
- After ovulation, LH stimulates the formation of the corpus luteum (yellow body), which produces progesterone to prepare the uterus for a potential pregnancy.
Effects in Men
- LH stimulates the Leydig cells in the testes to produce testosterone.
- Testosterone is essential for sperm production (spermatogenesis) and the development of male secondary sex characteristics.
Clinical Importance and LH Measurement
LH levels in blood or urine are frequently measured in clinical practice to detect hormonal disorders and assess fertility. Reference ranges vary depending on sex, age, and phase of the menstrual cycle.
Reference Values (Approximate)
- Women (follicular phase): approx. 2–15 IU/L
- Women (LH surge/ovulation): approx. 22–105 IU/L
- Women (luteal phase): approx. 0.6–19 IU/L
- Women (postmenopause): approx. 16–64 IU/L
- Men (adult): approx. 1.7–8.6 IU/L
Diseases and Disorders Associated with LH
Abnormal LH levels can indicate a variety of medical conditions or hormonal imbalances:
Elevated LH Levels
- Primary gonadal insufficiency (e.g., premature ovarian insufficiency, Klinefelter syndrome): The pituitary releases more LH in response to insufficient gonadal function.
- Polycystic ovary syndrome (PCOS): Often associated with an elevated LH-to-FSH ratio.
- Menopause: Physiologically elevated LH levels due to the loss of ovarian feedback.
Low LH Levels
- Hypothalamic or pituitary dysfunction (e.g., hyperprolactinemia, tumors, significant weight loss, excessive exercise): Reduced GnRH secretion leads to low LH levels.
- Hypogonadotropic hypogonadism: Insufficient LH release resulting in hormonal deficiency and impaired fertility.
Diagnostic Use
LH is measured through a routine blood test or a urine test (e.g., over-the-counter ovulation test kits). In fertility diagnostics, LH is always evaluated alongside FSH, estradiol, prolactin, and other hormones. The optimal timing of blood sampling in women depends on the phase of the menstrual cycle.
Therapeutic Relevance
Synthetic LH or LH-like compounds are used in reproductive medicine, for example in hormonal stimulation protocols for in vitro fertilization (IVF) and in the treatment of infertility. GnRH analogues are also used to deliberately control LH release, for instance in the treatment of endometriosis or prostate cancer.
References
- Styne DM, Grumbach MM. Physiology and Disorders of Puberty. In: Melmed S et al. (eds.): Williams Textbook of Endocrinology, 14th edition. Elsevier, 2020.
- World Health Organization (WHO). Laboratory Manual for the Examination and Processing of Human Semen. 6th edition. WHO Press, 2021. Available at: https://www.who.int
- Berga SL, Loucks TL. The diagnosis and treatment of stress-induced anovulation. Minerva Ginecologica. 2005;57(1):45-54. PubMed PMID: 15758865.
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