LH is often used in conjunction with other tests (FSH, testosterone, oestradiol and progesterone) in the investigation of infertility in both men and women. LH levels are also useful in the investigation of menstrual irregularities (irregular periods) and to aid in the diagnosis of pituitary gland disorders. In children, FSH and LH are used to diagnose delayed and precocious (early) puberty.

In women and men, LH (along with FSH) is requested as part of the investigation of infertility and pituitary disorders.

LH and FSH may be measured when a boy or girl does not appear to be entering puberty at an appropriate age (either too late or too soon).

In women, FSH and LH levels can help to tell the difference between primary ovarian failure (failure of the ovaries themselves) and secondary ovarian failure (failure of the ovaries due to disorders of either the pituitary gland or the hypothalamus in the brain). Increased levels of FSH and LH are consistent with primary ovarian failure. Some causes of primary ovarian failure are listed below.

Developmental defects:

• Ovarian agenesis (failure to develop ovaries)
• Chromosomal abnormality, such as Turner’s syndrome
• Ovarian steroidogenesis defect, such as 17 alpha hydroxylase deficiency

Premature ovarian failure due to: 

• Radiation therapy
• Chemotherapy
• Autoimmune disease

Chronic anovulation (failure to ovulate) due to:

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

When a woman enters the menopause and her ovaries stop working, FSH and LH levels will rise.

Low levels of FSH and LH are consistent with secondary ovarian failure due to a pituitary or hypothalamic problem.

In men, high FSH levels are due to primary testicular failure. This can be due to developmental defects in testicular growth or to testicular injury, as indicated below.

Developmental defects:

• Gonadal agenesis (failure to develop testes)
• Chromosomal abnormality, such as Klinefelter's syndrome

Testicular failure:

• Viral infection (mumps)
• Trauma
• Radiation therapy
• Chemotherapy
• Autoimmune disease
• germ cell tumour

Low levels of FSH are consistent with pituitary or hypothalamic disorders.

In young children, high levels of FSH and LH and development of secondary sexual characteristics at an unusually young age are an indication of precocious (early) puberty. This is much more common in girls than in boys.

About Reference Intervals

LH results can be increased with use of certain drugs, such as clomiphene and naloxone. LH results can decrease with oral contraceptives (the pill), phenothiazines and certain hormone treatments.

The basic test for infertility is measurement of progesterone to check that ovulation is occurring. Other tests for infertility include FSH and LH and other blood tests to assess your reproductive hormone levels. A post-coital test may be carried out where the cervical mucus is examined 2-8 hours after intercourse to check if the sperm are surviving in it. A hysterosalpingogram (image of fallopian tubes) may be done to see whether your fallopian tubes are blocked. Your partner may be asked to give a specimen of semen for analysis.

You may have polycystic ovary syndrome (PCOS), a hormonal problem seen in 5-10% of women of childbearing age and a major cause of infertility. With this condition, ovaries may become larger because of cysts that form in them. Women with PCOS also may have high levels of testosterone and do not ovulate normally. You may need to undergo several laboratory tests, including FSH, LH and testosterone, to make sure that PCOS is the condition causing your symptoms. A combination of medications and hormone therapy may help your symptoms.

Men also produce FSH and LH in their bodies, and these hormone levels are important for male reproduction too. In men, FSH stimulates the testes to produce sperm just as in women FSH stimulates the ovaries to produce eggs. In men, LH can be measured to investigate the cause of a low testosterone.