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Follicle Stimulating Hormone

Follicle stimulating hormone (FSH) secretion by the pituitary is under dual control by the hypothalamus and the gonads. The hypothalamus produces GnRH, which maintains basal FSH secretion. The testes and ovary produce inhibin, a hormone that inhibits FSH secretion.  In men, FSH stimulates Sertoli cells to undergo spermatogenesis.   In women, FSH stimulates ovarian follicle maturation and, together with LH, stimulates estrogen secretion and ovulation.

Measurement of serum FSH is useful in the work up of patients with delayed or precocious puberty, infertility, and pituitary disorders.  FSH levels are measured in infertility to distinguish primary failure of the ovary or testes from pituitary hypofunction.  FSH levels are decreased in patients with pituitary failure and increased in patients with ovarian disease. 

FSH concentration is included in fertility workups to assess ovarian reserve. High FSH concentration in the early part of the menstrual cycle is a predictor of reproductive aging. FSH is measured on day 2 or 3 of the menstrual cycle, early in the follicular phase. FSH values greater than 10 IU/L are highly specific in predicting poor response to ovarian stimulation, while FSH values greater than 18 IU/L are a predictor of poor pregnancy outcome.

Menopause is clinically defined as the absence of menses for 12 months. Natural menopause occurs at an average age of 51 years.  Approximately 1% of women become postmenopausal before 40 years of age and 5% become postmenopausal after 55 years of age.  During several years before menopause, serum levels of FSH increase and ovarian follicles abnormally mature.  As a result estrogen and progesterone levels become erratic.  Serum FSH levels >40 IU/L document with certainty that ovarian function has ceased.

FSH levels are elevated in men with primary testicular failure, castration, and Klinefelter’s syndrome.  FSH levels are elevated in women with menopause, ovariectomy, ovarian agenesis, and Turner’s syndrome.  FSH secreting pituitary tumors are rare and do not produce a distinct endocrine disorder. 

FSH levels are decreased in men with hypopituitarism, hypophysectomy, adrenal tumors, and testosterone medications.  In women, decreased FSH levels are seen in; hypopituitarism, hypophysectomy, adrenal or ovarian tumors, polycystic ovaries, Sheehan’s Syndrome, menstrual disorders, oral contraceptives, and estrogen therapy. 

Reference range is:

 

Gender

Reference Range IU/L

Male

<16

Female

Follicular

1 - 8

Ovulation

4 - 25

Luteal

1 - 5

Postmenopausal

40 - 100

 

Specimen requirement is one SST tube of blood.

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