Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) are chemical messengers produced by the pituitary gland, a small organ located at the base of the brain. They play a role in many bodily functions, contributing to overall health.
The Hormones LH and FSH Explained
LH and FSH are classified as gonadotropins, hormones that regulate the function of the gonads (ovaries in females and testes in males). They are produced by the pituitary gland, which receives signals from the hypothalamus through gonadotropin-releasing hormone (GnRH).
This communication forms the hypothalamic-pituitary-gonadal (HPG) axis, a feedback system that maintains hormone balance. When the hypothalamus releases GnRH, it stimulates the pituitary gland to secrete both LH and FSH. These hormones then travel through the bloodstream to the gonads, signaling them to produce reproductive hormones. The levels of these sex hormones are then monitored by the hypothalamus, which adjusts GnRH, LH, and FSH production in a negative feedback loop.
Their Essential Roles in Reproduction
In Females
In females, LH and FSH orchestrate the menstrual cycle, influencing follicular development and ovulation. At the beginning of the menstrual cycle, FSH stimulates the growth and maturation of ovarian follicles, each containing an immature egg. As these follicles develop, they produce estrogen, which helps thicken the uterine lining in preparation for pregnancy. A surge in LH, around mid-cycle, triggers ovulation, releasing the mature egg from the dominant follicle. LH also stimulates the remaining follicular cells to form the corpus luteum, which then produces progesterone to further prepare the uterus for implantation.
In Males
In males, LH and FSH are important for reproductive function. LH primarily stimulates the Leydig cells within the testes to produce testosterone. Testosterone is necessary for sperm production and the development of male characteristics. FSH acts on the Sertoli cells in the testes, which support spermatogenesis (sperm development). Both LH and FSH work in concert with testosterone to ensure sperm and male reproductive health.
Interpreting Normal Ranges
General Considerations
Normal ranges for LH and FSH vary by sex, age, and, for females, menstrual cycle phase. Laboratory reference ranges can also differ between facilities; always refer to the specific ranges provided with test results.
For Adult Males
For adult males, normal FSH levels range from 1.42 to 15.4 IU/L, and LH levels fall between 1.8 and 8.6 IU/L.
For Adult Females
Female LH and FSH levels fluctuate throughout the menstrual cycle. During the follicular phase (the first half of the cycle), FSH levels are between 1.37 and 9.9 IU/L, while LH levels are 1.68 to 15 IU/L. An LH surge occurs around mid-cycle, with levels reaching 10 to 75 IU/L, signaling ovulation. During the luteal phase (the second half of the cycle), FSH levels are between 1.09 and 9.2 IU/L, and LH levels range from 0.61 to 16.3 IU/L.
After Menopause
After menopause, FSH levels rise (19.3 to 100.6 IU/L) and LH levels are above 15 IU/L, as ovaries become less responsive.
When Levels Deviate From Normal
High Levels
When LH and FSH levels fall outside their ranges, it can indicate an underlying issue with the reproductive system or the glands that control these hormones. High levels of LH and FSH suggest a problem with the gonads themselves; the ovaries or testes are not producing enough sex hormones. This prompts the pituitary gland to produce more LH and FSH in an attempt to stimulate them, a condition referred to as primary hypogonadism. For example, in females, elevated levels could point to primary ovarian insufficiency or menopause. In males, high levels might indicate testicular failure due to injury, infection, or genetic conditions like Klinefelter syndrome.
Low Levels
Conversely, low levels of LH and FSH suggest a problem with the pituitary gland or the hypothalamus, which are not producing enough stimulating hormones. This condition is known as secondary hypogonadism. Low levels can lead to a reduction in sex hormone production by the gonads, resulting in delayed puberty, infertility, or menstrual irregularities in females and low testosterone in males. Causes can include pituitary tumors, significant weight loss, or excessive exercise. Consulting a healthcare professional is recommended for diagnosis and treatment.