Women:

In women, measurement of serum FSH is useful in patients to investigate irregular periods, to evaluate for menopause onset in certain age groups, as part of initial fertility workup testing, to evaluate for delayed or precocious puberty and to assess pituitary disorders.

High FSH concentration in the initial phases of the menstrual cycle, the follicular phase, is an early indicator of poor ovarian response for ovulation later on in that cycle. In menopause, two FSH levels >30, taken 6 weeks apart, can be an indicator of menopause. POI, or premature ovarian failure can occur post oophorectomy, post radiation or chemotherapy, or due to autoimmune conditions. It can also occur due to congenital absence or agenesis of the ovaries or in those with underlying genetic causes such as Turners syndrome, fragile X syndrome. 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.

Low levels of FSH are seen most commonly seen in conjunction with low LH and low GnRH and indicate a disruption of the hypothalamic pituitary ovarian axis – hypogonadotrophic hypopituitarism. This is a reversible condition often caused by excessive weight loss, exercise or stress. Low FSH also occurs in women on the oral combined contraceptive pill or those with PCOS.

Males :

In men, FSH levels are found to be decreased in men with hypopituitarism, adrenal tumours and those taking testosterone medication.  FSH is found to be increased if there is primary testicular failure as a result of gonadal agenesis or underlying genetic disorder which affects sexual development such as Klinefelters syndrome. Secondary testicular failure can occur after mumps infection, after traumatic injury, post chemotherapy or radiotherapy, from chronic alcohol abuse or if there is an underlying genetic disorder which affects sexual development such as Klinefelters syndrome.