Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

PRLPM
84462
PRL
cutoff results in a reduced specificity (approximately 40%), emphasizing the need for a combination of
different tests to assure accurate biochemical diagnosis. Patients with PC1/3 deficiency have low, or
sometimes undetectable, insulin levels and substantially elevated proinsulin levels, exceeding the upper
limit of the reference range substantially in the fasting state and rising even higher after food intake.
Many other hormonal abnormalities are also present, including cortisol deficiency (because of lack of
processing of pro-opiomelanocortin to adrenocorticotropic hormone and other peptides), infertility and,
often, morbid obesity. This assay demonstrates no cross-reactivity with insulin or C-peptide.
Reference Values:
3-20 pmol/L
Clinical References: 1. Kao PC, Taylor RL, Service FJ: Proinsulin by immunochemiluminometric
assay for the diagnosis of insulinoma. J Clin Endocrinol Metab 1994;78(5):1048-1051 2. Service FJ:
Hypoglycemic disorders. N Engl J Med 1995;322(17):1144-1152 3. Steiner DF: The proprotein
convertases. Cur Opin Chem Biol 1998;2(1):31-39 4. Vezzosi D, Bennet A., Fauvel J, Caron P: Insulin,
C-peptide and proinsulin for the biochemical diagnosis of hypoglycemia related to endogenous
hyperinsulinism. Eur J Endocrinol 2007;157(1):75-83
Prolactin, Pituitary Macroadenoma, Serum
Clinical Information: 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.
Useful For: 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)
Interpretation: 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.
Reference Values:
Males: 3-13 ng/mL
Females: 3-27 ng/mL
Clinical References: 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
Prolactin, Serum
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