FSH is often used in conjunction with other tests (LH, testosterone, estradiol, and progesterone) in the workup of infertility in both men and women. FSH levels are used to help determine the reason a man has a low sperm count. FSH levels are also useful in the investigation of menstrual irregularities and to aid in the diagnosis of pituitary disorders or diseases involving the ovaries or testes. In children, FSH and LH are used to diagnose delayed or precocious (early) puberty.

In women and men, FSH and LH are ordered as part of the workup of infertility and pituitary or gonadal disorders. FSH may be ordered to determine if a woman has reached menopause. In children, FSH and LH 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 females

growth of pubic hair

genitalia growth in males

beginning of menstruation in females.

If any or some of these signs appear at a younger than average age or are delayed beyond the expected age range for puberty, it may be an indication of a more serious problem involving the hypothalamus, pituitary, gonads (ovaries or testes) 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 women, FSH and LH levels can help to differentiate between primary ovarian failure (failure of the ovaries themselves) and secondary ovarian failure (failure of the ovaries due to disorders of either the pituitary or the hypothalamus). 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 
• Chemotherapy 
• Autoimmune disease

Chronic anovulation (failure to ovulate) due to: 

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

When a woman enters menopause and her ovaries stop working, FSH 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 
• Chromosomal abnormality, such as Klinefelters syndrome

Testicular failure:

• Viral infection (mumps) 
• Trauma 
• Radiation 
• Chemotherapy 
• Autoimmune disease 
• Germ cell tumor

Low levels are consistent with pituitary or hypothalamic disorders.

In young children, high levels of FSH and LH and/or 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 can have many different underlying causes that need to be diagnosed and treated. Some of the causes include:Central nervous system lesions

Hormone-secreting tumors

Ovarian tumors or cysts

Testicular tumors

Normal prepubescent levels of LH and FSH in children exhibiting some signs of pubertal changes may indicate 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 the age range of puberty. The test for LH response to GnRH may need to be performed along with other testing to diagnose the reason for the delayed puberty. Some of the causes for delayed puberty can include:

Gonadal (ovary or testes) failure (such as PCOS)

Hormone deficiency

Turner’s syndrome (chromosomal abnormality in girls)

Klinefelter’s syndrome (chromosomal abnormality in boys)

Chronic infections

Cancer

Eating disorder (anorexia nervosa)

FSH results can be increased with use of cimetidine, clomiphene, digitalis, and levodopa. FSH results can decrease with oral contraceptives, phenothiazines, and hormone treatments.

If you’ve recently had a nuclear medicine scan, the radioisotopes used in the scan may interfere with results of the FSH test.