Luteinizing Hormone (LH)

Luteinizing Hormone (LH) is a key hormone produced by the anterior pituitary gland in the brain. It plays a central role in the reproductive system for both men and women, helping regulate sex hormone production, ovulation, and fertility.

🧠 What Does LH Do?

🔹 In Women:

LH works together with follicle-stimulating hormone (FSH) to regulate the menstrual cycle and ovulation.

LH’s Roles:

• Triggers ovulation: A surge in LH levels mid-cycle causes the mature egg to be released from the ovary.
• Stimulates corpus luteum formation: After ovulation, LH helps transform the ruptured follicle into the corpus luteum, which produces progesterone — critical for maintaining early pregnancy.

🔹 In Men:

LH stimulates the Leydig cells in the testes to produce testosterone.

LH’s Roles:

• Maintains normal testosterone levels
• Supports sperm production indirectly (testosterone is required for spermatogenesis)
• Essential for puberty and male sexual development

💊 Medical Uses and Testing:

✅ LH Blood Tests Are Used To:

• Evaluate fertility or menstrual irregularities
• Diagnose polycystic ovary syndrome (PCOS)
• Detect pituitary or gonadal dysfunction
• Monitor ovulation timing for assisted reproduction
• Assess puberty timing (precocious or delayed puberty)
• Investigate low testosterone or infertility in men

📉 Low LH Levels May Indicate:

• Hypopituitarism (underactive pituitary)
• Hypothalamic dysfunction
• Stress, eating disorders, or excessive exercise
• Kallmann syndrome (genetic condition causing delayed puberty)
• Use of anabolic steroids (which suppress LH and testosterone)

📈 High LH Levels May Indicate:

• Ovulation (normal mid-cycle surge in women)
• Menopause
• Polycystic ovary syndrome (PCOS)
• Gonadal failure (e.g., testicular or ovarian failure)
• Certain pituitary tumors

🔁 LH and the Hormonal Feedback Loop:

In Men:

1. Hypothalamus releases GnRH (Gonadotropin-releasing hormone)
2. Pituitary releases LH and FSH
3. LH stimulates testosterone production from the testes
4. High testosterone sends a signal to the brain to decrease LH/FSH → a negative feedback loop

In Women:

1. LH is low during most of the cycle
2. Estrogen rises → triggers LH surge
3. LH surge triggers ovulation
4. After ovulation, LH helps form corpus luteum

🧪 Normal LH Ranges (approximate, varies by lab and age):

🧬 LH vs. hCG (Comparison):

🧠 Summary:

• LH is crucial for fertility, hormone production, and sexual development
• It triggers ovulation in women and testosterone production in men
• Abnormal LH levels can indicate hormonal imbalance, infertility, or pituitary issues
• Its role in the hormonal feedback system is tightly regulated