Prolactin: Normal Range, Causes of High Prolactin, and When to Image the Pituitary

Prolactin is made by lactotrope cells in the anterior pituitary. Unlike most pituitary hormones, prolactin's default state is "off", the hypothalamus actively suppresses it through dopamine. Anything that disrupts dopamine delivery to the pituitary (medications that block dopamine receptors, pituitary stalk compression, severe hypothyroidism that raises TRH) tends to disinhibit prolactin and raise levels.

Prolactin physiology has several useful properties:

• Pulsatile: varies hour to hour. Drawing in the morning, fasting, ideally after sitting quietly for 15 minutes, is good practice.
• Stress-responsive: venipuncture itself can raise levels modestly. A single mild elevation often normalizes on repeat.
• Macroprolactin: a biologically inactive prolactin-IgG complex can falsely elevate the assay. PEG precipitation testing rules this in or out.

Standard reference cutoffs:

• Adult women (non-pregnant): below 25 ng/mL.
• Adult men: below 20 ng/mL.
• Pregnancy: rises throughout, reaching 200–500 ng/mL at term.
• Lactation: 100–300 ng/mL with nursing; falls between feeds.
• Postmenopausal women: below 20 ng/mL.
• Children: below 20 ng/mL.

Severity grading for non-pregnant adults:

• 25–50 ng/mL: mildly elevated. Often medication, stress, or recent meal. Recheck.
• 50–100 ng/mL: moderate. Could be medication, microadenoma, hypothyroidism, or stalk effect.
• 100–250 ng/mL: microadenoma likely (microprolactinoma).
• Above 250 ng/mL: macroprolactinoma very likely.

The differential for hyperprolactinemia in a non-pregnant adult, in rough order of frequency:

• Medications: by far the most common cause of mild to moderate hyperprolactinemia.
  • Antipsychotics (especially risperidone, paliperidone, haloperidol; less so quetiapine, aripiprazole).
  • Metoclopramide, prochlorperazine, domperidone (dopamine receptor antagonists).
  • SSRIs (variable, usually mild).
  • Opioids, chronic use frequently raises prolactin.
  • Estrogen in high doses.
  • Methadone, tricyclic antidepressants.
  • Verapamil (rarely).
• Pituitary adenoma (prolactinoma): most common pituitary tumor type. Microadenoma (<10 mm) typical with prolactin 100–250; macroadenoma (≥10 mm) usually 250+. Prolactin >500 nearly always means macroprolactinoma.
• Hypothyroidism: primary hypothyroidism with high TSH and TRH disinhibits prolactin. Always check TSH in any hyperprolactinemia workup.
• Pituitary stalk compression / disconnection: non-prolactinoma pituitary mass cuts dopamine signal, modestly elevating prolactin (usually <100). MRI distinguishes from prolactinoma.
• Renal failure: reduced clearance.
• Liver cirrhosis: altered estrogen and dopamine metabolism.
• Polycystic ovary syndrome: mildly elevated prolactin in some patients; mechanism unclear.
• Chest wall stimulation: nipple stimulation, chest trauma, surgery, or zoster, neural reflex.
• Stress, recent meal, recent venipuncture: modest, transient elevation.
• Macroprolactin: biologically inactive complex; recognize and exclude with PEG testing before pursuing imaging.

Symptoms in women: amenorrhea, oligomenorrhea, infertility, galactorrhea (in 30–80%), low libido, decreased bone density. Symptoms in men: low libido, erectile dysfunction, infertility, decreased facial/body hair, gynecomastia. Macroadenomas also cause headaches, visual field defects (bitemporal hemianopia from optic chiasm compression), and hypopituitarism.

Low prolactin is rarely measured because it rarely matters clinically. When it does:

• Hypopituitarism: global pituitary dysfunction; low prolactin alongside low ACTH, TSH, LH/FSH, GH.
• Sheehan's syndrome: postpartum pituitary infarction; failure to lactate is one of the early signs.
• Dopamine agonist therapy: bromocriptine, cabergoline directly suppress prolactin. Used to treat prolactinoma; suppression is therapeutic, not pathologic.
• Pituitary surgery or radiation: direct damage to lactotrope cells.

An isolated low prolactin in an otherwise asymptomatic adult is usually unimportant.

A practical workup:

1. Confirm with a repeat draw in the morning, fasting, after 15 minutes of rest. Many borderline values normalize.
2. Rule out pregnancy in any reproductive-age woman.
3. Review medications carefully, antipsychotics, antiemetics, opioids, some antidepressants. Stopping (or switching when possible) for 4–6 weeks and rechecking is the standard maneuver.
4. Check TSH: primary hypothyroidism causes hyperprolactinemia and is fully reversible with thyroid replacement.
5. Check renal and hepatic function if relevant, creatinine, ALT, AST.
6. Consider macroprolactin testing if the elevation is unexpected and the patient is asymptomatic.
7. MRI of the pituitary when prolactin is persistently above 100 ng/mL with no medication or thyroid explanation, when prolactin is above 250 (macroprolactinoma threshold), or when symptoms point to a mass (headaches, visual changes).
8. Consider hook effect: extremely high prolactin (>10,000 ng/mL) in macroprolactinoma can saturate the assay and falsely report a low value. Ask for serial dilution if a large pituitary mass is found with a deceptively normal prolactin.

• Prolactin above 100 ng/mL with no medication or thyroid cause: order pituitary MRI; refer to endocrinology.
• Prolactin above 250 ng/mL: macroprolactinoma highly likely; MRI, endocrinology referral, often visual field testing.
• Visual field defect, persistent headache, or progressive cranial nerve symptoms with elevated prolactin: urgent imaging.
• Postpartum failure to lactate plus amenorrhea: consider Sheehan's; check pituitary axis broadly.
• Patient on antipsychotic with new sexual dysfunction or amenorrhea: check prolactin; consider regimen adjustment with prescriber.
• Reproductive-age woman with secondary amenorrhea: prolactin is part of the standard workup along with TSH, FSH, LH, estradiol.
• Mild elevation (25–50) with obvious cause, recheck after addressing cause; imaging not required initially.

• TSH: always check; primary hypothyroidism causes reversible hyperprolactinemia.
• FSH and LH: usually low in hyperprolactinemia (suppressed by prolactin's effect on GnRH).
• Estradiol in women, testosterone in men, assess gonadal consequences.
• Creatinine: renal failure raises prolactin.
• ALT / AST: assess liver function in significant elevations.
• hCG: confirm or exclude pregnancy.
• MRI of the pituitary: definitive imaging for adenoma.
• Macroprolactin (PEG precipitation): when prolactin is elevated but no symptoms support it.