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Unit Code 87843:
Macroprolactin, Serum

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Useful For

Determining biologically active levels of prolactin, in

asymptomatic patients with elevated prolactin levels

 

Ruling out the presence of macroprolactin

Clinical Information

Prolactin is secreted by the anterior pituitary gland under negative

control by dopamine, which is secreted by the hypothalamus. The

only physiological function of prolactin is the stimulation of milk

production. In normal individuals, the prolactin level rises in

response to physiologic stimuli such as nipple stimulation, sleep,

exercise, sexual intercourse, and hypoglycemia. Pathologic causes

of hyperprolactinemia include prolactin-secreting pituitary adenoma

(prolactinoma), diseases of the hypothalamus, primary hypothyroidism,

section compression of the pituitary stalk, chest wall lesions, renal

failure, and ectopic tumors.

 

Hyperprolactinemia may also be caused by the presence of a high-

molecular-mass complex of prolactin called macroprolactin (typically

due to prolactin bound to immunoglobulin). In this situation, the patient

is asymptomatic. Hyperprolactinemia attributable to macroprolactin

is a frequent cause of misdiagnosis and mismanagement of patients.

Macroprolactin should be considered if, in the presence of elevated

prolactin levels, signs and symptoms of hyperprolactinemia are

absent, or pituitary imaging studies are not informative.

Reference Values

TOTAL PROLACTIN       

      Males    

            < or = 18 years: not established

            > 18 years: 4.0 - 15.2 ng/mL 

      Females

            < or = 18 years: not established

            > 18 years : 4.8 - 23.3 ng/mL

 

Percent of the precipitated (complexed) prolactin fraction of the total prolactin

            <50% (considered negative for macroprolactin)

 

Unprecipitated prolactin levels are expected to be within the total prolactin

reference range.

Interpretation

When the percentage of the precipitated prolactin (complexed)

fraction of total prolactin is <50%, the specimen is considered

negative for macroprolactin. When total prolactin exceed the

upper reference limit and macroprolactin is negative, other

causes for hyperprolactinemia should be explored.

 

When the percentage of the precipitated (complexed) prolactin

fraction of total prolactin is > or = to 50%, the specimen is considered

positive for the presence of macroprolactin.

 

Following macroprolactin precipitation, a patient whose

unprecipitated prolactin level is greater than the upper limit

of the total prolactin reference range may have hyperprolactinemia.

 

See #8690 "Prolactin, Serum" for interpretation of prolactin levels.

Cautions

Demonstration of the presence of macroprolactin does not

exclude the possibility of concomitant presence of pituitary

adenoma. Results should be interpreted in conjunction with

clinical findings.

Clinical Reference

1. Fahie-Wilson M:  In hyperprolactinemia, testing for macroprolactin

     is essential. Clin Chem 2003;49(9):1434-1436

 

2. Gibney J, Smith TP, McKenna TJ:  Clinical relevance of macro-

     prolactin. Clin Endocrinol 2005;62:633-643

Key