Prolactin Blood Test

What is prolactin?

Prolactin is a hormone made by the anterior pituitary gland, located at the base of the brain. Its primary function is to stimulate and maintain breast milk production (lactation) after childbirth. In men and non-pregnant women, prolactin is present in small amounts. Levels naturally rise during pregnancy and breastfeeding. Elevated prolactin (hyperprolactinaemia) outside of pregnancy suppresses reproductive hormones, causing infertility and other symptoms.

Prolactin normal range

When is a pituitary MRI needed?

A prolactin level above 100 ng/mL strongly suggests a prolactinoma and warrants a pituitary MRI to look for a tumour. Levels of 25–100 ng/mL can have many causes (medications, hypothyroidism, stress) and are investigated based on clinical context. Very high levels (>500 ng/mL) almost always indicate a large prolactinoma (macroprolactinoma).

Treatment of prolactinoma

Most prolactinomas are treated with dopamine agonist medications, cabergoline or bromocriptine, which are highly effective at lowering prolactin and shrinking the tumour. Surgery is rarely needed. Regular prolactin monitoring is used to track treatment response.

Questions to ask your doctor

• Should I have a pituitary MRI?
• Is a medication causing my high prolactin?
• Should I check my thyroid (TSH)?
• Can high prolactin be treated with medication alone?
• Will my fertility return once prolactin is normalised?

Frequently asked questions

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Hyperprolactinemia. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK537331

References

Sources cited on this page. PubMed links open the original abstract.

1. Melmed S, Casanueva FF, Hoffman AR, et al. Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(2):273–288. PMID 21296991 · doi:10.1210/jc.2010-1692

What causes a raised prolactin – and when to investigate further

Prolactin is secreted by the pituitary gland and is normally elevated during pregnancy and breastfeeding. Outside of these states, hyperprolactinaemia (raised prolactin) requires investigation. The most important distinction is between physiological/pharmacological causes – which are common – and a pituitary prolactinoma, which is the commonest pituitary tumour and requires specific treatment.

Common pharmacological causes include dopamine antagonists: antipsychotics (haloperidol, risperidone, olanzapine), metoclopramide, domperidone, and many antidepressants. Because dopamine tonically inhibits prolactin secretion, anything that blocks dopamine receptors raises prolactin. In a patient on antipsychotics with a mildly raised prolactin and no symptoms, drug-induced hyperprolactinaemia is the most likely explanation and does not require MRI. However, if prolactin is markedly elevated (>5000 mU/L or >200 ng/mL) or symptoms are prominent, MRI of the pituitary should be performed regardless of medication status.

Macroprolactin – a common false positive

Macroprolactinaemia occurs when prolactin circulates bound to IgG antibodies, forming a large inactive complex. Immunoassays detect these complexes and report a falsely elevated prolactin, even though biologically active prolactin is normal. Macroprolactinaemia is found in approximately 15–25% of patients referred for hyperprolactinaemia and typically causes no symptoms. Most laboratories now screen all elevated prolactin results with polyethylene glycol (PEG) precipitation to detect macroprolactin before further investigation – a normal monomeric prolactin after PEG precipitation rules out clinically significant hyperprolactinaemia.

Treating prolactinomas – dopamine agonists as first-line

Unlike most pituitary tumours, prolactinomas typically shrink dramatically with medical treatment rather than surgery. Dopamine agonists – cabergoline (first choice) or bromocriptine – normalise prolactin in 85–90% of patients and reduce tumour size in most macroprolactinomas (tumours >10 mm). Cabergoline is preferred because of its once- or twice-weekly dosing and lower rate of side effects (nausea, postural hypotension). The European Society of Endocrinology and Pituitary Society guidelines recommend surgery only for dopamine agonist resistance or intolerance, or for emergency decompression when vision is threatened.