Luteinizing Hormone (LH) is a protein secreted by the pituitary gland, located at the base of the brain. It is one of two main gonadotropins, working alongside Follicle-Stimulating Hormone (FSH) to regulate the reproductive system. LH levels fluctuate significantly depending on a female’s life stage and the specific phase of the menstrual cycle. Monitoring these levels provides medical insight into fertility, ovarian function, and the onset of menopause.
The Role of Luteinizing Hormone in the Female Body
LH plays a direct part in the complex processes that govern the monthly reproductive cycle in females. Its actions are primarily focused on the ovaries, where it facilitates the maturation and release of an egg. Throughout the first half of the cycle, LH works with FSH to stimulate the growth of ovarian follicles, which contain the developing eggs.
As the dominant follicle grows, it produces increasing amounts of estrogen. When estrogen reaches a certain threshold, it signals the pituitary gland to abruptly increase LH secretion. This rapid increase is known as the LH surge, which directly triggers ovulation and typically lasts 24 to 48 hours.
The spike causes the mature follicle to rupture and release the egg into the fallopian tube, marking the transition into the second half of the menstrual cycle.
Following ovulation, the ruptured follicle transforms into the corpus luteum. LH stimulates the corpus luteum to produce progesterone, which prepares the uterine lining for a potential pregnancy.
If conception does not occur, LH levels decrease, leading to the degeneration of the corpus luteum. This drop in progesterone causes the uterine lining to shed, beginning menstruation and restarting the cycle.
Normal Reference Ranges by Life Stage
Luteinizing hormone levels are measured in International Units per Liter (IU/L) or milli-International Units per Milliliter (mIU/mL). Because the hormone fluctuates, a single measurement is less informative than the context of the reading relative to the cycle or life stage. Although laboratory reference ranges can vary, the pattern of LH change across the cycle is consistently observed.
Follicular Phase (Early Cycle)
During the follicular phase, which starts with menstruation and lasts until ovulation, LH levels are relatively low. Typical blood serum measurements range approximately from 1.68 to 15 IU/L. This level supports the initial growth and maturation of the ovarian follicles.
Ovulatory Peak (LH Surge)
The defining characteristic of LH is its dramatic spike just before ovulation. This ovulatory peak, or surge, causes levels to rise significantly, often reaching between 21.9 and 56.6 IU/L, though some clinical ranges report values as high as 76.3 IU/L. The surge is a short-lived event, usually lasting only a day or two, signaling that an egg is about to be released.
Luteal Phase (Post-Ovulation)
Immediately after the surge and ovulation, LH levels drop back down to a lower, more stable range. During the luteal phase, measurements are typically between 0.61 and 16.3 IU/L. This post-ovulation level is sufficient to sustain the corpus luteum’s progesterone production.
Post-Menopause
Once a female reaches menopause, the ovaries stop responding to hormonal signals from the pituitary gland. In an attempt to stimulate the non-responsive ovaries, the pituitary gland continuously releases high amounts of LH and FSH. Consequently, post-menopausal LH levels are persistently elevated, commonly falling between 14.2 and 52.3 IU/L.
Pre-Puberty
In young girls before the onset of puberty, the reproductive axis is largely dormant, resulting in very low LH concentrations. These baseline levels are typically below 0.5 IU/L, reflecting the lack of ovarian activity at this stage of development. As puberty approaches, LH levels begin to gradually increase, initiating the physical changes associated with sexual maturation.
Causes of Elevated or Suppressed Levels
Levels of LH outside of the expected ranges for the menstrual cycle or life stage can indicate an underlying medical condition. Generally, abnormal results are categorized based on whether the issue originates in the ovaries (primary) or in the brain’s control centers—the hypothalamus and pituitary gland (secondary).
High LH Causes
LH levels consistently high outside of the normal ovulatory surge or post-menopausal state often point to a failure of the ovaries to produce sufficient estrogen and progesterone. This condition is termed primary ovarian insufficiency (POI). In POI, the pituitary gland attempts to compensate for the lack of ovarian feedback by producing more LH and FSH.
Polycystic Ovary Syndrome (PCOS) is another common condition that can present with elevated LH. In many cases of PCOS, the ratio of LH to FSH is disproportionately high, which contributes to irregular periods and infertility. This imbalance disrupts the normal follicular development necessary for ovulation.
Genetic conditions, such as Turner syndrome, can also cause the ovaries to function incorrectly or not develop fully. Since the ovaries cannot provide hormonal feedback, the pituitary gland continuously releases high levels of LH in an effort to stimulate them. This persistent elevation is a clinical sign of ovarian dysfunction.
Low LH Causes
Consistently suppressed LH levels suggest a problem with the production or release of the hormone from the pituitary gland or the signaling from the hypothalamus. Low levels are often seen in cases of hypothalamic amenorrhea, a condition where menstruation ceases due to issues originating in the brain’s hormone control center.
Factors such as severe calorie restriction, malnutrition, or excessive exercise can disrupt hypothalamic signaling. The body interprets these stressors as non-optimal for reproduction, leading to a shutdown of LH production. This results in insufficient LH to initiate follicle growth and trigger ovulation.
Low LH can also be a symptom of pituitary dysfunction, where the gland is unable to manufacture or release the hormone effectively. Conditions like Kallmann syndrome, a genetic disorder affecting reproductive hormone systems, are also associated with low LH production. The resulting lack of LH means the ovaries are not stimulated, leading to a failure of reproductive maturation or function.
How LH Levels Are Measured
LH levels are quantified using two primary methods for clinical and at-home monitoring. The most precise method is a blood serum test, which provides a quantitative measurement of the hormone concentration in IU/L or mIU/mL. This laboratory test is usually ordered by a healthcare provider to diagnose reproductive disorders or assess overall hormone status.
Blood testing requires careful timing relative to the menstrual cycle, as results are only meaningful when interpreted in context. For instance, a high LH reading is expected during the mid-cycle surge but would be abnormal during the follicular phase. Multiple blood draws may be necessary to fully understand the pattern of LH secretion.
The second method involves using urine-based ovulation predictor kits (OPKs), which are qualitative tests used for at-home tracking. These kits detect the presence of LH in the urine, indicating that the LH surge is in progress. The results are typically a positive or negative reading, signaling that ovulation is likely to occur within the next 24 to 36 hours.
While OPKs are a practical tool for fertility awareness, they do not provide the exact numerical concentration of the hormone like a blood test does. The urine test is designed to identify the surge threshold, making it a useful, non-invasive way to pinpoint the most fertile window.