Pathology Handbook

Macroprolactin

Synonyms

MPRL

Clinical Indications

Macroprolactin is the term used to describe a complex of serum prolactin with an IgG antibody. This larger form of prolactin has been recognised for a number of years and is found in some patients with increased serum prolactin levels.  Such patients, on follow-up, have usually been found to show no characteristics of the hyperprolactinaemic syndrome (infertility, menstrual irregularity, galactorrhoea). Whereas monomeric prolactin is bioactive, macroprolactin is considered biologically inactive. 

The combination of apparent hyperprolactinaemia (due to macroprolactin) and reduced bioactivity in vivo may cause diagnostic confusion and lead to inappropriate treatment. Studies have shown that in approximately 15% of patients with raised serum prolactin the major reactive species was macroprolactin. 
Most laboratory assays for prolactin  measure the prolactin component of macroprolactin.  Since macroprolactin remains in the serum for longer than monomeric prolactin this leads to apparently high circulating levels of prolactin. 

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Availability

Analysed if specific criteria met.

Specific Criteria

All samples with increased serum prolactin will be examined for the presence of macroprolactin. 

Turnaround Time

3 to 5 days

Specimen

Serum

Volume

1 mL

Container

Vacutainer gold top

Interpretation

If macroprolactin is detected a monomeric (bioactive) prolactin level will be calculated and reported as well as the total prolactin.