The test for luteinizing hormone (LH), a hormone associated with reproduction and the stimulation of the release of an egg from the ovary (ovulation) in women and testosterone production in men, has several uses.

In both women and men, LH is often used in conjunction with other tests (FSH, testosterone, estradiol and progesterone):

• In the workup of infertility
• To aid in the diagnosis of pituitary disorders that can affect LH production
• To help diagnose conditions associated with dysfunction of the ovaries or testicles

In women, LH levels are useful:

• In the investigation of menstrual irregularities
• To evaluate LH levels during the menstrual cycle; multiple urine LH tests may be ordered for this purpose. These LH "spot tests" can be performed at home and used to detect the surge in LH that indicates that ovulation will occur in the next 1-2 days. The tests can help determine when a woman is likely to be the most fertile.

In children, FSH and LH are used to diagnose delayed and precocious (early) puberty. Irregular timing of puberty may be an indication of a more serious problem involving the hypothalamus, the pituitary gland, the ovaries or testicles, or other systems. The measurement of LH and FSH may differentiate between benign symptoms and true disease. Once it is established that symptoms are a result of true disease, further testing can be done to discern the underlying cause.

In persons with evidence of poor ovarian or testicular function, LH is sometimes measured in response to administration of gonadotropin releasing hormone (GnRH) to distinguish between disorders involving the hypothalamus or pituitary gland. GnRH is the hormone produced by the hypothalamus that stimulates the pituitary to release LH and FSH. For this test, a baseline blood sample is drawn and then the person is given an injection of GnRH. Subsequent blood samples are drawn at specified times and the level of LH is measured. This test can help differentiate between a disorder of the pituitary (secondary), when LH will not respond to GnRH, or hypothalamus (tertiary), when LH responds to GnRH. It is also often helpful in the evaluation of precocious or delayed puberty.

In adults, LH (and FSH) tests may be ordered when:

• A woman is having difficulty getting pregnant or has irregular or an absence of menstrual periods
• When it is suspected that a women has entered menopause and her menstrual cycle has stopped or become irregular
• When a man's partner cannot get pregnant, when he has a low testosterone level, or when he has low muscle mass or decreased sex drive, for example.
• When a health practitioner suspects that a pituitary disorder is present; a pituitary disorder can affect the production of several different hormones so there may be signs and symptoms in addition to infertility that can include fatigue, weakness, unexplained weight loss, and decreased appetite to name a few.

In children, LH and FSH may be ordered when a boy or girl does not appear to be entering puberty at an appropriate age (either too late or too soon). Signs of puberty may include:

• Breast enlargement in girls
• Growth of pubic hair
• Growth of testicles and penis in boys
• Beginning of menstruation in girls

In Women

LH and FSH levels can help to differentiate between primary ovarian failure (failure of the ovaries themselves or lack of ovarian development) and secondary ovarian failure (failure of the ovaries due to disorders of either the pituitary or the hypothalamus).

Increased levels of LH and FSH are seen in primary ovarian failure. Some causes of primary ovarian failure are listed below.

Developmental defects:

• Failure to develop ovaries (ovarian agenesis)
• Chromosomal abnormality, such as Turner syndrome
• Defect in steroid production by the ovaries, such as 17 alpha hydroxylase deficiency

Premature ovarian failure due to:

• Exposure to radiation
• Chemotherapy
• Autoimmune disease

Chronic failure to ovulate (anovulation) due to:

• Polycystic ovary syndrome (PCOS)
• Adrenal disease
• Thyroid disease
• Ovarian tumor

In women who are trying to become pregnant, multiple LH tests can be used to detect the surge that precedes ovulation. An LH surge indicates that ovulation has occurred.

During menopause, a woman's ovaries cease to function; thus LH levels will rise.

Low levels of LH and FSH are seen in secondary ovarian failure and indicate a problem with the pituitary or hypothalamus. See the article on Pituitary Disorders for more information.

In Men

High LH levels may indicate primary testicular failure. This can be due to developmental defects in testicular growth or to testicular injury, as described below.

Developmental defects:

• Failure to develop gonads (gonadal agenesis)
• Chromosomal abnormality, such as Klinefelter syndrome

Testicular failure:

• Viral infection (mumps)
• Trauma
• Exposure to radiation
• Chemotherapy
• Autoimmune disease
• Germ cell tumor

Low levels of LH and FSH are seen in secondary failure of the testicles and indicate a problem with the pituitary or hypothalamus. See the article on Pituitary Disorders for more information.

In Both Men and Women

LH response to GnRH can help differentiate between secondary dysfunction (failure of the pituitary) and tertiary disorder (a problem involving the hypothalamus). Once the baseline level of LH has been measured, a dose of GnRH is given by injection. A subsequent increase in the level of LH indicates that the pituitary responded to the GnRH and points to a disorder involving the hypothalamus. A reduced level of LH shows that the pituitary did not respond to the GnRH and suggests a disease involving the pituitary.

In Children

In young children, high levels of LH and FSH with the development of secondary sexual characteristics at an unusually young age are an indication of precocious puberty. This is much more common in girls than in boys. This premature development is usually due to a problem with the central nervous system andcan have a few different underlying causes. Examples include:

• Central nervous system tumor
• Brain injury, trauma
• Inflammation within the central nervous system (e.g., meningitis, encephalitis)
• Brain surgery

Normal prepubescent levels of LH and FSH in children exhibiting some signs of pubertal changes may indicate a condition call "precocious pseudopuberty." The signs and symptoms are brought on by elevated levels of the hormones estrogen or testosterone. This may be caused by:

• Hormone-secreting tumors
• Adrenal gland tumors
• Ovarian tumors or cysts
• Testicular tumors

Normal FSH and LH levels with a few signs of puberty can also be a benign form of precocious puberty with no underlying or discernable cause or may just be a normal variation of puberty. In delayed puberty, LH and FSH levels can be normal or below what is expected for a youth within this age range. The test for LH response to GnRH in addition to other testing may help to diagnose the reason for the delayed puberty. Some of the causes for delayed puberty can include:

• Failure of the ovaries or testicles
• Hormone deficiency
• Turner syndrome 
• Klinefelter syndrome
• Chronic infections
• Cancer
• Eating disorder (anorexia nervosa)

Some drugs can cause LH to increase, such as anticonvulsants, clomiphene, and naloxone, while others cause LH to decrease, such as digoxin, oral contraceptives, and hormone treatments.

A recent nuclear medicine scan may interfere with results of the LH test if it is measured by a radioimmunoassay, which is seldom used any more.

LH is sometimes referred to as interstitial cell stimulating hormone (ICSH) in males.