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Luteinizing Hormone (LH)

Luteinizing Hormone (LH) is a glycoprotein released by the anterior pituitary in response to gonadotropin releasing hormone (GnRH) from the hypothalamus. LH is composed of an alpha subunit that is identical to the alpha subunit of TSH, FSH and hCG, and a beta subunit which gives it specificity.

Secretion of LH occurs in different patterns. The major pattern in males is tonic. Gonadal steroids exhibit negative feedback to inhibit secretion of LH and FSH. A cyclic pattern is present in females in which increased plasma estrogens exhibit positive feedback and stimulate the release of LH and FSH during ovulation. LH acts on the developing follicle to stimulate androgen production, which is the precursor of estradiol. There is a fall in FSH antecedent to the surge and then both gonadotropins peak at midcycle. A third pattern of secretion, pulsatile, occurs in males and females and is independent of blood concentration of gonadol steroids or gonadotropins.

Low or absent LH (hypogonadism) may be primary, secondary or tertiary. Primary hypogonadism is characterized by decreased steroid secretion and increased LH, FSH and GnRH due to removal of the negative feedback. Secondary hypogonadism (pituitary) results in decreased FSH and LH levels. Tertiary hypogonadism is caused by decreased GnRH. LH levels may be increased in cases of gonadal lesions.

The reference ranges are:

Males

mIU/L

Prepuberty

<0.5

Adult

2 - 12

Females

Prepuberty

<0.2

Follicular

1 - 18

Midcycle

24 - 105

Luteal

0.4 - 20

Postmenopausal

15 - 62

Specimen requirement is one SST tube of blood.

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