LH (Luteinizing Hormone)

Function

Luteinizing Hormone (LH) is a gonadotropin produced by the anterior pituitary gland. In both men and women, it is essential for reproduction. In women, an acute rise of LH—the 'LH surge'—triggers ovulation and development of the corpus luteum. In men, LH stimulates Leydig cells in the testes to produce testosterone.

Why it is Ordered

Healthcare providers order this test to investigate infertility, evaluate menstrual irregularities, or diagnose disorders of the pituitary gland or hypothalamus. In pediatrics, it is used to evaluate precocious or delayed puberty. It is also a core component of the workup for Polycystic Ovary Syndrome (PCOS).

Associated Conditions

• Polycystic Ovary Syndrome (PCOS): Often characterized by a high LH to FSH ratio.
• Primary Ovarian Failure: High LH levels as the body tries to stimulate non-responsive ovaries.
• Hypogonadism: Low levels may indicate pituitary or hypothalamic dysfunction (secondary hypogonadism), while high levels suggest testicular or ovarian failure (primary hypogonadism).
• Menopause: Naturally elevated LH levels due to the cessation of ovarian feedback loops.

Clinical Importance

Understanding LH levels helps clinicians map the Hypothalamic-Pituitary-Gonadal (HPG) axis. Because LH is secreted in pulses, a single measurement is often interpreted alongside FSH, Estradiol, or Testosterone to provide a complete picture of hormonal health.