Hyperprolactinemia Associated with Pituitary Adenoma

At a Glance

Hyperprolactinemia is the most common endocrine disorder of the hypothalamic-pituitary unit. In premenopausal women, hyperprolactinemia causes hypogonadism leading to symptoms of infertility, oligomenorrhea or amenorrhea, and galactorrhea. Hyperprolactinemia is often clinically silent in postmenopausal women who, by definition, are already hypogonadal. In men, hyperprolactinemia causes hypogonadism manifested by decreased libido, impotence, infertility, and, rarely, galactorrhea.

Prolactin-secreting pituitary adenomas are a relatively common cause of hyperprolactinemia and account for 30-40% of all pituitary adenomas, nearly all of which are benign. Depending on its size, the adenoma itself may cause signs and symptoms, including visual field abnormalities, blurred vision, and headache.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The measurement of serum prolactin is necessary to identify hyperprolactinemia. Testing can be performed without regard to time of day, because routine daily activities have little influence on prolactin concentration.

Prolactin concentrations correlate fairly well with the size of the adenoma. Microadenomas (<1 cm in diameter) are typically associated with a prolactin concentation less than 200 ng/mL. Macroadenomas (>1 cm in diameter) often yield higher concentrations that often exceed 1,000 ng/mL.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Prolactin concentrations that are slightly greater than the reference interval should be confirmed by repeat testing on a new blood sample, because prolactin may be influenced by strenuous exercise, emotional or physical stress, or rigorous stimulation of breast tissue.

Some prolactin immunoassays are susceptible to the high-dose hook effect such that the prolactin result is falsely decreased in the presence of a very elevated concentration of prolactin.

Several medications are known to cause hyperprolactinemia (see chapter on Anterior Pituitary, Hyperprolactinemia Associated with Drugs). Such medications should be ruled-out as potential causes of hyperprolactinemia prior to investigating organic causes.

Macroprolactin is a complex of prolactin and IgG and is a source of hyperprolactinemia in some individuals. Becuase of its high molecular mass, macroprolactin has prolonged clearance that can cause an apparant hyperprolactinemia. In the absence of clinical symptoms, hyperprolactinemia due to macroprolactin can cause clinical confusion. It is important to be aware that macroprolactinemia can coexist with true hyperprolactinemia.

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