Luteinizing Hormone (LH) is a protein hormone produced by the anterior pituitary gland. Classified as a gonadotropin, it stimulates the gonads (ovaries in females and testes in males) to produce hormones necessary for sexual function and fertility. In women, LH triggers the release of a mature egg from the ovary, known as ovulation. In men, the hormone stimulates specialized cells in the testes to produce testosterone, which is required for sperm production.
The Role of LH in the Menstrual Cycle
The level of LH naturally fluctuates throughout the menstrual cycle, with a temporary spike representing a normal “high” reading. The cycle begins with the follicular phase, where LH levels are relatively low, typically ranging from 1.9 to 15 milli-international units per milliliter (mIU/mL) in the blood serum. LH works alongside Follicle-Stimulating Hormone (FSH) to encourage the growth and maturation of ovarian follicles.
As a dominant follicle matures, it secretes increasing amounts of estrogen, which triggers a cascade of hormonal events. This rise in estrogen signals the pituitary gland to release a large, rapid burst of LH, known as the LH surge. The LH surge prompts the ovary to release the egg, initiating ovulation approximately 24 to 36 hours later.
During this ovulatory phase, LH levels peak, often soaring into a mid-cycle range between 21.9 and 56.6 mIU/mL. After ovulation, the cycle transitions into the luteal phase, and LH levels quickly fall back to their baseline. LH then supports the corpus luteum, the remnant of the follicle, to produce progesterone.
Interpreting High LH Readings
Defining what constitutes a “high” LH reading depends on the timing of the test and the method used for measurement. For at-home testing using ovulation prediction kits (OPKs), “high” is a visual interpretation based on the test line’s intensity. These urine tests are designed to detect the LH surge by comparing the test line’s color to a control line.
A positive result occurs when the test line is equal to or darker than the control line. This qualitative result typically corresponds to a urinary LH concentration that has crossed a manufacturer’s predetermined threshold. The ideal concentration threshold for predicting ovulation is often between 25 and 30 mIU/mL, though commercial kits may use a sensitivity anywhere from 20 to 50 mIU/mL.
In a clinical setting, interpreting a high LH reading from a blood serum test requires nuance and must be considered in the context of the menstrual cycle and other hormone levels. A sustained LH level above the non-ovulatory follicular phase range (approximately 1.9 to 15 mIU/mL) is considered elevated and warrants further investigation. For instance, a blood level persistently above 10 to 15 mIU/mL during the early follicular phase is flagged as abnormally high.
This sustained elevation outside the brief ovulatory window signals an underlying issue rather than a normal physiological event. Because LH is released in pulsatile bursts, a single blood sample may not capture the true average level. Therefore, a physician typically looks at LH in combination with FSH, estradiol, and a patient’s symptoms for an accurate diagnosis.
Medical Conditions Associated with Elevated LH
A persistent high LH level outside the normal mid-cycle surge signals dysfunction within the reproductive system’s feedback loop. One primary reason for chronic LH elevation is Primary Ovarian Insufficiency (POI) or menopause. In these conditions, the ovaries stop functioning effectively, leading to a significant drop in the production of ovarian hormones like estrogen.
Because the ovaries are no longer producing adequate hormone levels, the pituitary gland loses the negative feedback signal that normally keeps LH and FSH in check. In a compensatory effort to stimulate the non-responsive ovaries, the pituitary gland dramatically increases its output of gonadotropins, including LH. This condition, known as hypergonadotropic hypogonadism, results in postmenopausal LH levels that can range between 5.0 and 55.2 mIU/mL.
Polycystic Ovary Syndrome (PCOS)
Another common cause of sustained high LH is Polycystic Ovary Syndrome (PCOS), which is characterized by a hormonal imbalance. Women with PCOS frequently exhibit an elevated ratio of LH to FSH. While the normal follicular phase ratio is typically close to 1:1, the ratio in PCOS can be 2:1 or even 3:1.
This sustained, elevated LH level overstimulates ovarian cells, leading to excessive production of androgens (male hormones). The combination of elevated LH and high androgens disrupts follicular maturation, often preventing ovulation and contributing to the syndrome’s characteristic symptoms.