- Prolactin is a hormone made by the pituitary gland, best known for its role in breast milk production.
- A prolactin test is a simple blood test often ordered for irregular periods, fertility questions, breast discharge, or certain symptoms.
- Reference ranges and units vary by lab and differ for pregnancy and breastfeeding, so results are read against your lab's range.
- High prolactin has many possible causes, including some medications, stress, and a benign pituitary growth called a prolactinoma.
- Low prolactin is less commonly a concern but can occasionally point to pituitary issues.
- A clinician interprets your result with your symptoms and history — do not self-diagnose.
A prolactin test is a simple blood test that measures the level of prolactin, a hormone in your body. It is often ordered when a clinician is looking into symptoms such as irregular periods, difficulty getting pregnant, or unexpected breast changes. This guide explains what prolactin does, what high and low levels may suggest, and why the number always needs to be interpreted by a clinician in the context of your health rather than on its own.
What is prolactin, and what does the test measure?
Prolactin is a hormone produced mainly by the pituitary gland, a small gland at the base of the brain. It is best known for stimulating breast milk production during and after pregnancy, but everyone makes some prolactin. The test measures how much prolactin is circulating in your blood at the time the sample is taken. Levels naturally rise in pregnancy and breastfeeding, and can also change with sleep, stress, exercise, and even a recent meal, which is why timing and preparation can matter.
When is a prolactin test ordered?
A clinician may order a prolactin test to help investigate:
- Irregular, infrequent, or absent menstrual periods
- Difficulty becoming pregnant (as part of a fertility work-up)
- Milky nipple discharge that is not related to breastfeeding
- Certain symptoms such as unexplained headaches or vision changes, when a pituitary cause is being considered
- Low libido or, in men, erectile difficulties that may have a hormonal component
It is one piece of a larger picture and is usually considered alongside other tests and your medical history. In some cases, prolactin is checked as part of investigating symptoms that could have several explanations, so a normal result can be just as useful as an abnormal one for helping a clinician narrow things down.
Sometimes a lab will also look at whether a raised result reflects “macroprolactin,” a larger, biologically less active form of the hormone that can make levels appear high without causing symptoms. This is another reason an unexpectedly high reading is often confirmed with a repeat or specialized test before any conclusions are drawn.
Understanding results: ranges and what they may suggest
Reference ranges and units vary between laboratories, and separate ranges apply during pregnancy and breastfeeding, so always compare your result with the range on your own report. In broad terms:
| Result | Some possible considerations | What usually follows |
|---|---|---|
| Within the reference range | Typically not a source of concern on its own | Clinician interprets with your symptoms |
| Higher than the range (hyperprolactinemia) | Medications, stress, pregnancy or breastfeeding, hypothyroidism, or a benign pituitary growth (prolactinoma) | May prompt repeat testing, medication review, or imaging |
| Lower than the range | Less often a concern; occasionally linked to pituitary underactivity | Interpreted in context; sometimes further evaluation |
Because so many everyday factors can nudge prolactin up, a single elevated reading is often rechecked before any conclusions are drawn. For a sense of how another common blood test is used and why context matters, see how another common blood test is used.
Why a clinician must interpret your result
A prolactin number means little without the rest of your story. Your clinician weighs your symptoms, medications, other hormone levels, and history to decide what a result means and whether any follow-up is needed. Some medications commonly raise prolactin, and stress or the blood draw itself can too, so results are read carefully. A borderline or one-time high value often means very little, whereas a clearly and repeatedly elevated result may warrant more attention. Please do not diagnose yourself or change any medication based on a prolactin value. Our evidence-first wellness guides emphasize working with a qualified professional for anything involving diagnosis or treatment.
Preparing for the test
Your provider may ask you to have the blood drawn at a particular time of day, since prolactin follows a daily rhythm and is often higher after sleep. You may be asked to avoid heavy exercise or stress beforehand, and to mention any medications and supplements you take. Follow the specific instructions from your provider or lab, and tell them if you are or could be pregnant or breastfeeding.
Frequently asked questions
Does high prolactin mean I have a tumor? Not necessarily. High prolactin has many causes, including medications and stress. A benign pituitary growth is one possibility your clinician may investigate, often with repeat testing or imaging.
Can medications raise my prolactin? Yes. Several common medications can increase prolactin, which is why a full medication review is part of interpreting results.
Why does my range differ from someone else’s? Labs use different assays and units, and ranges differ in pregnancy and breastfeeding. Always use your own lab’s range.
Is a low prolactin level a problem? Usually it is not a major concern, but your clinician will interpret it alongside your symptoms and other results.
Do I need to fast? Fasting is not always required, but timing and rest may matter. Follow your provider’s instructions.
Should I interpret the result myself? No. Prolactin should be interpreted by a clinician in the context of your overall health.
This article is for general education and is not medical advice. Supplements and therapies affect people differently and can interact with medications or conditions. Talk to your doctor, pharmacist, or a licensed clinician before making changes to your health routine.
Sources
- MedlinePlus — prolactin blood test overview and what results may mean
- Mayo Clinic — prolactinoma and pituitary information
- National Institutes of Health (NIH) — hormone and pituitary health resources
- U.S. National Library of Medicine — laboratory test references