The Luteinizing Hormone (LH) test is a blood test that measures the amount of LH in your bloodstream. LH is a key reproductive hormone made by the pituitary gland (a small gland at the base of the brain) that helps control the ovaries in females and the testes in males. Because LH is closely tied to ovulation, menstrual cycles, testosterone production, and fertility, measuring LH levels can provide important clues about reproductive and pituitary function.

In people with ovaries, LH rises and falls throughout the menstrual cycle. A mid-cycle “LH surge” triggers ovulation (release of an egg). In people with testes, LH helps stimulate the testes to produce testosterone and supports sperm production.

Results are interpreted based on age, sex, menstrual cycle timing (if applicable), and whether you are pregnant or using hormonal medications. In general terms:

High LH may suggest that the ovaries or testes are not responding normally (so the pituitary produces more LH to “push” them), or it may reflect a normal LH surge near ovulation. Persistently high LH can be seen around menopause, in some fertility disorders (such as PCOS), or with primary ovarian/testicular failure.

Low LH may suggest reduced signaling from the pituitary/hypothalamus (the brain’s hormone control centers), which can lead to irregular periods, lack of ovulation, low testosterone, or infertility.

Because LH works closely with other hormones, it is often checked alongside FSH (follicle-stimulating hormone), estradiol, progesterone, testosterone, and sometimes prolactin and thyroid tests to get a complete picture.

A clinician may order an LH (luteinizing hormone) test when symptoms or health goals point to possible issues with ovulation, fertility, puberty development, or pituitary function. Common reasons include:

Fertility evaluation and ovulation tracking

LH testing can help determine whether and when ovulation is occurring. It may be used in a fertility workup for people who are trying to conceive, especially with irregular cycles or suspected anovulation (not ovulating). (At-home ovulation predictor kits measure LH in urine; the lab test measures LH in blood.)

Irregular menstrual cycles or missed periods

It may be ordered for irregular periods, absent periods (amenorrhea), very frequent periods, or unusual cycle changes, to help identify hormonal causes such as polycystic ovary syndrome (PCOS), premature ovarian insufficiency, or hypothalamic/pituitary problems.

Symptoms of hormone imbalance

In females: acne, excess facial/body hair, scalp hair thinning, weight changes, or difficulty getting pregnant may prompt LH testing, often as part of an evaluation for PCOS or other endocrine disorders.

In males: low sex drive, erectile dysfunction, infertility, decreased muscle mass, fatigue, or low testosterone symptoms may prompt LH testing to help distinguish testicular causes from pituitary causes.

Puberty concerns in children/teens

LH testing may be used when puberty starts unusually early (precocious puberty) or is delayed (delayed puberty), helping clinicians understand whether the brain’s hormonal signaling is turning on too soon, too late, or not at all.

Possible pituitary or hypothalamic disorders

If there are concerns about pituitary function—such as multiple hormone deficiencies, headaches with vision changes, or abnormal results on other hormone tests—LH can help assess pituitary output and guide further testing.

Menopause or ovarian reserve questions

LH may be checked (often with FSH and estradiol) when evaluating symptoms of perimenopause/menopause or suspected premature ovarian insufficiency. LH can rise as ovarian function declines.

• Polycystic ovary syndrome (PCOS)
• Anovulation (not ovulating) and other ovulatory disorders
• Infertility (female and male factor infertility evaluation)
• Primary ovarian insufficiency (premature ovarian failure)
• Menopause and perimenopause
• Primary testicular failure (hypergonadotropic hypogonadism)
• Hypogonadotropic hypogonadism (hypothalamic or pituitary causes of low sex hormones)
• Pituitary adenoma or other pituitary disorders affecting hormone production
• Hyperprolactinemia (often evaluated alongside LH/FSH)
• Precocious puberty
• Delayed puberty

• Tracking ovulation to time intercourse or fertility treatments (supporting conception planning)
• Identifying causes of irregular periods and supporting cycle regulation plans
• Evaluating fertility and guiding next steps (e.g., additional hormone tests, imaging, referral)
• Assessing reproductive hormone balance in suspected PCOS (alongside other labs)
• Monitoring menopause transition and understanding symptoms related to changing hormones
• Evaluating low testosterone symptoms and supporting men’s reproductive health goals
• Assessing pituitary gland function as part of a broader endocrine health check
• Supporting puberty and growth-development evaluations when timing is atypical