Prolactin, Pituitary Macroadenoma, Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Prolactin is secreted by the anterior pituitary gland. The major chemical controlling prolactin secretion is hypothalamic dopamine, which inhibits pituitary prolactin secretion.
In normal individuals, the prolactin level rises in response to physiologic stimuli, such as sleep, exercise, nipple stimulation, sexual intercourse, hypoglycemia, postpartum period, and birth. Pathologic causes of hyperprolactinemia include prolactin-secreting pituitary adenoma (prolactinoma), functional and organic disease of the hypothalamus, primary hypothyroidism, section compression of the pituitary stalk, chest wall lesions, renal failure, and ectopic tumors. Prolactinomas are 5 times more frequent in females than males.
Prolactin-secreting macroadenomas (>10 mm in diameter) can sometimes produce exceedingly high serum prolactin concentrations that may paradoxically result in falsely-low prolactin concentrations when measured by immunometric assays. In such situations, very high concentrations of prolactin saturate both the capture and signal antibodies in the assay, block formation of the capture antibody-prolactin-signal antibody "sandwich," and result in falsely-decreased prolactin results (referred to as the high-dose hook effect). With such tumors, serum prolactin levels may be falsely decreased into the normal reference interval, potentially resulting in inappropriate patient management. Dilution of the specimen eliminates the analytic artifact in these cases.
Identifying patients with pituitary macroprolactinomas
Quantifying prolactin in specimens where the high-dose hook effect is suspected (eg, presence of pituitary adenoma with symptoms of prolactinoma, and lower than expected prolactin level)
Significantly increasing concentrations of prolactin, obtained after dilution of the serum, is consistent with high concentrations of prolactin secreted by functional macroprolactinomas.
Serum prolactin levels >250 ng/mL are usually associated with prolactin-secreting tumors, whereas moderately increased levels of serum prolactin are not a reliable guide for determining whether a prolactin-producing pituitary adenoma is present.
Slight nonlinearities detected in the prolactin dilution series may indicate interference by macroprolactin (prolactin bound to immunoglobulin). In these situations, patients are asymptomatic. Apparent hyperprolactinemia attributable to macroprolactin is a frequent cause of misdiagnosis and mismanagement of patients.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test is not useful for initial patient assessment; order PRL / Prolactin, Serum as the initial screening test.
A pituitary adenoma should be identified by imaging studies prior to ordering this test.
A macroadenoma may be nonfunctional and not secrete prolactin.
Infrequently, a patient may have a nonfunctional macroadenoma but apparent hyperprolactinemia caused by the presence of macroprolactin. To determine this, order MCRPL / Macroprolactin, Serum.
Multiple medications can cause a rise in prolactin levels, including phenothiazines and other anti-psychotic drugs, metoclopramide, opiates, amphetamines, alpha-methyl dopa, estrogen, and cimetidine.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Males: 3-13 ng/mL
Females: 3-27 ng/mL
Clinical References Provides recommendations for further in-depth reading of a clinical nature
St-Jean E, Blain F, Comotois R: High prolactin levels may be missed by immunoradiometric assay in patients with macroprolactinomas. Clin Endocrinol 1996 Mar;44(3):305-309