Prolactin is a pituitary hormone primarily known for stimulating milk production. Beyond breastfeeding, prolactin testing helps evaluate menstrual disorders, infertility, galactorrhea (inappropriate milk production), and potential pituitary tumors. The prolactin test is straightforward but interpretation requires attention to common factors that affect levels. This guide covers prolactin testing, normal ranges, and clinical applications.
What prolactin does
Prolactin is produced by lactotrophs in the pituitary gland. Functions include:
- Milk production (lactation) in women
- Possible roles in immune function and other processes
Prolactin is normally suppressed by dopamine from the hypothalamus. Anything that decreases this dopaminergic inhibition raises prolactin.
Reference ranges
- Non-pregnant women: under 25 ng/mL
- Men: under 20 ng/mL
- Pregnancy: progressive elevation, up to 200-300 ng/mL at term
- Lactating women: variable
Causes of elevated prolactin
Physiological:
- Pregnancy
- Lactation
- Stress
- Sleep
- Recent breast stimulation
Medications (very common cause):
- Antipsychotics (risperidone particularly)
- Some antidepressants
- Metoclopramide
- Cimetidine
- Estrogens
- Methyldopa
Pathological:
- Prolactinomas (pituitary tumors producing prolactin)
- Other pituitary tumors compressing dopaminergic inhibition
- Hypothyroidism (TRH stimulates prolactin)
- Chronic kidney disease (impaired clearance)
- Polycystic ovary syndrome (mild elevations)
Prolactinoma evaluation
Prolactin levels suggesting prolactinoma:
- Above 200 ng/mL: macroprolactinoma very likely
- 100-200 ng/mL: microprolactinoma possible, evaluate
- 25-100 ng/mL: many causes; medications and other factors first
Confirmed elevated prolactin (after ruling out medications, hypothyroidism, kidney disease) typically requires brain MRI to evaluate for pituitary tumor.
Treatment approaches
Prolactinomas are typically treated with dopamine agonists (cabergoline, bromocriptine), which usually shrink tumors and normalize prolactin. Surgery is reserved for cases not responding to medication or with specific complications.
Medication-induced hyperprolactinemia is managed by addressing the offending medication when possible, or accepting elevated prolactin if the medication is necessary.
Frequently Asked Questions
How should prolactin be drawn?
Morning, fasting if possible, after avoiding stress and breast stimulation. Strenuous exercise and sex shortly before testing can affect results.
Can stress affect prolactin?
Yes. Mild elevations from venipuncture stress are common.
What does mild prolactin elevation mean?
Many causes. Medications, stress, and benign causes are most common. Repeat testing and clinical context guide further evaluation.
Should I get an MRI for elevated prolactin?
Generally yes if prolactin is significantly elevated and reversible causes (medications, hypothyroidism, kidney disease) are excluded.
Can prolactin cause infertility?
Yes. Elevated prolactin can suppress reproductive hormones and cause anovulation in women, decreased libido and erectile dysfunction in men.
The bottom line on the prolactin test
Prolactin testing helps evaluate menstrual disorders, infertility, galactorrhea, and potential pituitary tumors. Many causes of elevation exist, with medications being among the most common. Marked elevations warrant pituitary imaging. Discuss results with your endocrinologist for proper evaluation.