Macroprolactin Check
Label Mnemonic: MPRO
Epic Lab Code: LAB7438
Downtime Form: A-1a General Laboratory Requisition
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
Minimum:
3 mL whole blood light green top tube or TWO Microtainer® devices.
Testing Schedule:
Monday-Friday batch analysis.
Turn Around Time:
24 hours (upon receipt in laboratory)
Reference Range:
MALES: 4.0 to 15.2 ng/mL FEMALES: 4.8-23.3 ng/mL
Comments:
The macroprolactin check will only be run on samples that have prolactin concentration above the upper limit of the gender-specific reference range. If prolactin concentration is within or below the gender-specific reference range, the macroprolactin result will be credited and only the prolactin concentration reported. If the prolactin concentration is above the appropriate reference range, the prolactin concentration will be determined with and without treatment with polyethylene glycol (PEG). A decrease of greater than 50% when precipitated with polyethylene glycol indicates the possible presence of macroprolactin and the macroprolactin result will be resulted as "POSITIVE".
Test Limitations:
The assay is unaffected by icterus (bilirubin is less than 30 mg/dL), hemolysis = 1500 (Hb is less than 1 g/dL), lipemia (Intralipid is less than 1500 mg/dL) and biotin is less than 100 ng/mL (criterion: recovery within plus or minus 10% of initial value).

In patients receiving therapy with high biotin doses (i.e. is greater than 5 mg/day) no sample should be taken until at least 8 hours after the last biotin administration.

No interference was observed from rheumatoid factor (up to approx. 1700 U/mL) and samples from dialysis patients.

No high dose hook effect at prolactin concentrations of 12690 ng/mL.

In vitro tests were performed on 17 commonly used pharmaceuticals.

No interference with the assay was found.

As with all tests containing monoclonal antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or who have received them for diagnostic purposes. In rare cases, interference due to extremely high titers of antibodies to ruthenium can occur.

Prolactin contains additives which minimize these effects.

Extremely high titers of antibodies to streptavidin can occur in isolated cases and cause interference.

When determining prolactin it should be remembered that the measured concentration is dependent upon when the blood sample was taken, since the secretion of prolactin occurs in episodes and is also subject to a 24-hour cycle. The release of prolactin is promoted physiologically by suckling and stress. In addition, elevated serum prolactin concentrations are caused by a number of pharmaceuticals (especially dopamine receptor antagonists including antipsychotics), TRH and estrogen.

The release of prolactin is inhibited by dopamine, L-dopa and ergotamine derivatives.

A number of publications report the presence of macroprolactin in the serum of female patients with various endocrinological diseases or during pregnancy.(1,2) Differing degrees of detection of the serum macroprolactins (ultra-big is greater than 160 kD) relative to monomeric prolactin (22-23kD) by various immuno-assays have also been described. This could make the detection of hyperprolac tinemia dependent on the immunoassay used.

The prolactin assay also encompasses macroprolactin. Accordingly, higher values may occasionally be found in patient samples than with other assay procedures.

For diagnostic purposes, the prolactin findings should always be assessed in conjunction with the patient's medical history, clinical examination and other findings.

(1) Dericks-Tan JSE, Siedentopf HG, Taubert HD. Discordant Prolactin
    Values obtained with Different Immunoassays in an infertile
    Patient. J Lab Med 1997;21(9):465-470.

(2) Leite V, Cosby H, Sobrinho LG, Fresnoza A, Santos MA, Friesen HG.
    Characterization of big-big prolactin in patients with
    hyperprolactinoma. Clin Endocrinol 1992;37:365-372.
Methodology:
Electrochemiluminescence Immunoassay
CPT Code:
84146