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Prolactin, Monomeric, Serum or Plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of monomeric (single-molecule) prolactin in your blood. Prolactin is a hormone made by the pituitary gland that plays a role in breast development and milk production.

Quick summary

["Monomeric prolactin testing helps your doctor determine whether an elevated prolactin level is due to the active, single-form hormone or to larger, less active forms."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
78995-8
Short code
Prolactin.monomeric/Prolactin % SerPl
Synonyms
Prolactin.monomeric/Prolactin % SerPl
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
2
Ref high
18
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84146
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What Is Prolactin?

Prolactin is a hormone produced mainly by the pituitary gland, a small gland at the base of your brain. It supports breast development and milk production in women and plays a role in other body functions in both men and women. Levels are normally kept in a balanced range by signals from the brain.

Why Measure the Monomeric Form?

In the blood, prolactin can circulate in different forms. Monomeric prolactin is the single-molecule form that is biologically active. Sometimes prolactin can clump together into larger forms, such as "big" or "macro" prolactin, which may register as high on a standard test but do not act the same way in the body. Measuring the monomeric form specifically can help clarify whether a high prolactin result reflects the active hormone.

How the Test Is Done

A healthcare professional collects a blood sample, usually from a vein in your arm, into a tube. The sample is sent to a laboratory, where it is analyzed to measure the level of monomeric prolactin. Your care team will tell you if any special preparation, such as timing the sample or avoiding certain activities beforehand, is needed.

What the Results Mean

Results are interpreted by your healthcare provider in the context of your symptoms, medications, and medical history. A measurement of the monomeric form can help distinguish between true elevation of active prolactin and the presence of larger, less active forms. Your provider will explain what your result means for your situation; this page does not provide specific numeric ranges because they vary by laboratory.

Reference range

Adult males: 2-18 ng/mL; Females: 2-29 ng/mLN/A

Specimen: serum

For females: inform if menstrual cycle status. For certain tests, timing within menstrual cycle may matter.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Prolactin testing is used to evaluate symptoms such as unexpected milk production, irregular or absent menstrual periods, breast tenderness, reduced libido, or infertility. It can also help assess pituitary function and monitor certain conditions. Measuring the monomeric fraction is particularly useful when a standard prolactin result is elevated but symptoms are mild or absent, because it can help identify cases where a high reading is due mainly to less active larger forms. Your healthcare provider will interpret results alongside your history and may recommend follow-up testing.

Short name

Monomeric Prolactin

Frequently asked questions

Do I need to fast for this test?
Fasting is often not required for a prolactin test, but preparation can vary by laboratory and by your provider's instructions. Follow the specific directions you are given. Because factors like stress, sleep, and recent activity can affect prolactin, your provider may suggest timing the sample in a particular way.
Can medications affect my prolactin result?
Yes. Several types of medications can raise or lower prolactin levels. Tell your healthcare provider about all medicines, supplements, and hormones you take so your result can be interpreted correctly. Do not stop any medication on your own without talking to your provider first.
What is the difference between monomeric prolactin and a regular prolactin test?
A regular prolactin test measures total prolactin in the blood, which can include both the single-molecule (monomeric) form and larger combined forms. A monomeric prolactin test focuses on the active single-molecule form. This distinction can help your provider better understand whether a high total prolactin level reflects active hormone in the body.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy