Hyperprolactinaemia: causes, workup, and treatment in AU general practice

Prolactin is a pituitary hormone whose principal role is initiating and sustaining lactation. Outside of pregnancy and breastfeeding, persistently elevated prolactin — hyperprolactinaemia — signals a disturbance worth investigating. Prevalence in general practice is higher than many clinicians expect: among women presenting with oligo/amenorrhoea, hyperprolactinaemia is found in roughly 15–20%.

The Endocrine Society of Australia endorses a systematic approach that begins with excluding the reversible causes — medication, hypothyroidism, pregnancy — before attributing a finding to a pituitary lesion. This matters because most elevated prolactin results in a GP setting have a benign, often correctable explanation.

The clinical consequences of untreated pathological hyperprolactinaemia are driven primarily by hypogonadism: oestrogen deficiency in women (amenorrhoea, infertility, bone loss, vasomotor symptoms) and testosterone deficiency in men (low libido, erectile dysfunction, infertility). Galactorrhoea — spontaneous or expressed milky nipple discharge unrelated to the puerperium — occurs in around 80% of hyperprolactinaemic women but is less common in men.

When treatment is indicated and the cause is a prolactinoma, the condition generally responds well to dopamine agonist therapy. Most patients are managed in a shared-care arrangement between general practice and endocrinology.

A. Core clinical — the AU general practice framework

Who to test

Therapeutic Guidelines recommend checking prolactin in:

• Women with unexplained oligomenorrhoea, amenorrhoea, or infertility
• Anyone with galactorrhoea unrelated to pregnancy or breastfeeding
• Men with unexplained hypogonadism — low libido, erectile dysfunction, or infertility where testosterone is also low
• Patients on long-term antipsychotics or antiemetics who develop menstrual irregularity or sexual side effects
• Headache with visual field disturbance (bitemporal hemianopia suggests macroadenoma with chiasmal compression — this is an urgent presentation)
• As part of any pituitary incidentaloma workup

Step one: exclude reversible causes

Before attributing an elevated prolactin to a pituitary adenoma, the RACGP recommends systematic exclusion of:

1. Physiological causes — pregnancy (β-hCG), breastfeeding, nipple stimulation, vigorous exercise, stress, post-orgasm state; sample timing matters and fasting morning blood reduces noise
2. Pharmacological causes — D2 antagonist antipsychotics (risperidone, amisulpride, paliperidone raise prolactin most; olanzapine modestly; quetiapine, aripiprazole, and clozapine minimally); antiemetics (metoclopramide, prochlorperazine, domperidone); SSRIs (modest); opioids (chronic use); H2 antagonists (cimetidine); high-dose oestrogens
3. Primary hypothyroidism — TRH stimulates prolactin release; TSH is always checked alongside prolactin
4. Chronic kidney disease — reduced prolactin clearance; U&E and eGFR are part of the initial panel
5. Macroprolactinaemia — biologically inactive PRL–IgG complex that elevates the immunoassay result without causing clinical disease

Macroprolactinaemia — the common benign mimic

Macroprolactinaemia accounts for up to 30% of incidentally elevated prolactin results. The key clinical clue is a laboratory elevation with absent or discrepant symptoms. The Australian Pituitary Foundation notes that patients are sometimes investigated with MRI before this common diagnosis is excluded.

The laboratory confirms macroprolactinaemia using polyethylene glycol (PEG) precipitation: PEG binds the large immunoreactive complex; if monomeric (bioactive) prolactin after precipitation falls within the normal range, macroprolactinaemia is confirmed. No imaging is required. No dopamine agonist. Reassurance and periodic rechecking is the approach.

Workup sequence for confirmed pathological hyperprolactinaemia

Repeat the test as a fasting morning sample before initiating workup — a single elevated result is frequently physiological.

If the repeat confirms true pathological elevation:

1. Bloods: TSH ± free T4, β-hCG, U&E/eGFR, macroprolactin PEG precipitation if asymptomatic or discrepant
2. Medication review: switch or withdraw the offending drug; recheck prolactin in 4–6 weeks before proceeding
3. MRI pituitary with contrast (gadolinium) — the gold standard; differentiates microprolactinoma (under 10 mm), macroprolactinoma (10 mm or larger), and stalk compression from other sellar masses
4. Full pituitary axis (particularly with macroadenoma): morning cortisol ± short Synacthen test, free T4, LH, FSH, testosterone (men) or oestradiol (women), IGF-1 (to exclude co-secretory acromegaly), sodium and urine osmolality
5. Visual field testing (Humphrey perimetry) if tumour ≥10 mm or near the optic chiasm

The hook effect

Very large prolactinomas producing extreme prolactin concentrations (over 100,000 mIU/L) can paradoxically return a falsely low or normal immunoassay result because of antibody saturation — the “hook effect.” If a macroadenoma is found but prolactin appears only mildly elevated or normal, request a serial dilution assay from the laboratory before concluding the tumour is non-functioning.

B. Prolactinoma: evidence and treatment

When treatment is indicated

Not every elevated prolactin requires pharmacotherapy. Therapeutic Guidelines recommend treatment when:

• Symptoms of hypogonadism are present (amenorrhoea, infertility, sexual dysfunction)
• Galactorrhoea is causing distress
• Mass effect exists — visual compromise or cranial nerve involvement
• Bone loss attributable to hypogonadism is occurring

An asymptomatic microprolactinoma with mild prolactin elevation and preserved gonadal function can reasonably be observed rather than treated, with annual prolactin and periodic MRI.

Cabergoline — first-line

The Webster 1994 New England Journal of Medicine randomised controlled trial established cabergoline as superior to bromocriptine across efficacy, tolerability, and dosing convenience. The Endocrine Society 2011 guideline and the Pituitary Society 2023 consensus statement both endorse cabergoline as the preferred first-line agent for prolactinoma.

Dose: Start 0.25 mg twice weekly with food; titrate to 0.5–1 mg twice weekly against prolactin response. Some patients require up to 2–3.5 mg/week. PBS Authority Required (Streamlined) for prolactinoma.

Efficacy: Normalises prolactin in 80–90% of microadenomas and 70–80% of macroadenomas. Tumour volume reduction of 50–80% over 6–12 months is typical in responders.

Side effects to discuss with every patient:

• Nausea, postural hypotension, headache — usually mild and early; food co-ingestion reduces nausea
• Impulse control disorders — gambling, hypersexuality, compulsive shopping or eating; a class effect of D2 agonists. Counsel patients before starting and enquire specifically at every review visit
• Cardiac valvulopathy — this is a concern at the very high cumulative doses used in Parkinson’s disease; at standard prolactinoma doses (≤2 mg/week) the risk is low; a baseline echocardiogram is appropriate before sustained doses exceeding 2 mg/week

Withdrawal after sustained remission: After prolactin has been normal for at least 2 years on treatment, specialist-guided withdrawal can be attempted. Approximately 25–30% of patients sustain remission off treatment; annual surveillance post-withdrawal is standard.

Bromocriptine — when to prefer it

The Australian Medicines Handbook lists bromocriptine (2.5–15 mg/day in divided doses) as a PBS-listed alternative. It is less well-tolerated than cabergoline — higher rates of nausea and postural hypotension — but carries a longer published pregnancy safety record, making it the dopamine agonist of choice in women who require continued therapy during pregnancy.

Surgery

Transsphenoidal surgery is reserved for specific situations:

• Macroadenoma with mass effect unresponsive to medical therapy
• Intolerance or resistance to all dopamine agonists
• Cystic prolactinoma (less responsive to pharmacotherapy)
• Pituitary apoplexy — haemorrhage or infarction into the adenoma; this is an emergency presentation requiring immediate neurosurgical assessment
• Selected pre-pregnancy debulking in macroadenoma — individualised decision made with endocrinology and neurosurgery

Pituitary surgery requires a specialist pituitary surgeon and is coordinated through multidisciplinary teams at major tertiary centres.

C. Pituitary incidentaloma

Advances in brain imaging have made pituitary incidentaloma a common clinical finding — approximately 10% of pituitary MRIs identify an incidental abnormality. Most are small non-functioning microadenomas. Rathke’s cleft cysts and craniopharyngiomas are other incidental sellar lesions encountered.

Initial hormone evaluation

The Pituitary Society 2023 consensus recommends that every pituitary incidentaloma undergo systematic hormone screening in both directions:

Overactivity screen: prolactin (prolactinoma), IGF-1 (acromegaly), overnight dexamethasone suppression or 24-hour urinary free cortisol (Cushing’s), TSH and free T4 (rare TSH-secreting adenoma), LH and FSH (usually non-functioning gonadotrophinoma)

Underactivity screen: morning cortisol ± short Synacthen test, free T4 + TSH, testosterone and LH/FSH (men), oestradiol + LH/FSH (women), IGF-1

Visual field testing (Humphrey perimetry) applies to any incidentaloma ≥10 mm or located close to the optic chiasm.

Management by size and function

Tumour characteristics	Management
Non-functioning microadenoma under 10 mm, asymptomatic	Observe: annual MRI for 3 years, then less frequent if stable; lifelong surveillance
Functioning adenoma (any size)	Specific treatment — cabergoline for prolactinoma; surgery for other functioning subtypes
Macroadenoma ≥10 mm	Endocrinology and neurosurgery referral; surgery if mass effect, chiasmal compression, or hypopituitarism
Aggressive features — rapid growth or atypical pathology	Multidisciplinary tertiary referral

One important distinction: stalk effect from a non-functioning adenoma compressing the pituitary stalk causes modest prolactin elevation, typically under 2,000 mIU/L, through disinhibition of dopaminergic tone. The correct treatment targets the underlying tumour — a dopamine agonist is not the appropriate response to stalk-mediated mild hyperprolactinaemia.

D. Australian operations

MBS and specialist referral pathways

Standard GP consultation items (23/36/44) apply. The prolactin assay is included in standard biochemistry pathology panels. MRI pituitary with contrast (MBS Item 63558) requires a specialist referral for Medicare funding in most circumstances — a relevant practical step once pathological hyperprolactinaemia is confirmed and GP-initiated initial workup is complete.

Specialist referral pathways in Australia:

• Endocrinologist — all confirmed pathological hyperprolactinaemia; prolactinoma management; incidentaloma with axis dysfunction
• Neurosurgeon (pituitary specialist) — macroadenoma requiring surgery; pituitary apoplexy emergency
• Ophthalmologist — visual field assessment and ongoing monitoring for macroadenoma
• Reproductive endocrinologist / fertility specialist — fertility planning in the setting of prolactinoma
• Psychiatrist — antipsychotic-induced hyperprolactinaemia where medication change is needed; this decision must not be made unilaterally at general practice level

Pituitary multidisciplinary teams operate at major Australian tertiary centres including Royal Prince Alfred (Sydney), Royal Melbourne, Royal Brisbane and Women’s, Flinders Medical Centre, and Royal Perth Hospital.

PBS prescribing

Per TGA prescribing information:

• Cabergoline (Cabaser, Dostinex — 0.5 mg tablets): PBS Authority Required (Streamlined) for hyperprolactinaemia and prolactinoma
• Bromocriptine (Parlodel — 2.5 mg tablets, 10 mg capsules): PBS Authority Required; Pregnancy Category A
• Levothyroxine — General Schedule; when primary hypothyroidism is the driving cause, treatment with levothyroxine normalises prolactin without requiring dopamine agonists

Bone health and monitoring

Sustained hypogonadism from untreated hyperprolactinaemia leads to bone loss that is clinically significant and often underrecognised. DEXA bone densitometry (MBS Items 12306/12320) is appropriate when hypogonadism has been present for an extended period. Adequate calcium and vitamin D sufficiency supports bone health throughout treatment. Once prolactin normalises and gonadal function restores, bone density typically improves but may not fully recover in those with prolonged exposure.

Patient education resources

HealthDirect — Prolactinoma and the Better Health Channel provide plain-language overviews useful to share with patients at diagnosis. The Australian Pituitary Foundation offers peer support, detailed patient guides, and a specialist directory — a particularly valuable resource for patients newly diagnosed with a prolactinoma who benefit from connecting with others managing the same condition.

E. Special populations

Adolescents. Hyperprolactinaemia presenting with delayed menarche or irregular cycles in a teenager warrants full workup including medication review — antipsychotic use for youth mental health conditions is a common culprit. Reference ranges differ from adult values and paediatric endocrinology input is appropriate for confirmed cases.

Pregnancy — microprolactinoma. Cabergoline or bromocriptine is generally stopped on confirmation of pregnancy. Microprolactinomas rarely grow significantly during pregnancy. Women are counselled to report new headache or visual symptoms promptly; MRI without gadolinium can be performed if symptoms arise. Most pregnancies in women with microprolactinoma proceed without complication.

Pregnancy — macroprolactinoma. Management is individually planned with endocrinology and may include continued dopamine agonist therapy, visual field monitoring each trimester, and in some cases pre-pregnancy surgical debulking. Bromocriptine has a longer published safety record in pregnancy than cabergoline and is generally preferred when continued medication is required.

Men. Men typically present later than women because symptoms of low libido and erectile dysfunction are attributed to other causes or go unreported. Bone loss is often established by the time of diagnosis. Testosterone may be considered alongside prolactin-lowering treatment when hypogonadism has been sustained, though prolactin normalisation itself generally restores the hypothalamic-pituitary-gonadal axis.

Older adults. Pituitary incidentaloma becomes more prevalent with age. Hormone screening principles are unchanged, but clinical goals are shaped by comorbidity and life expectancy — a non-functioning microadenoma in an older person with multiple medical conditions may warrant a different surveillance interval and intensity than in a younger person.

Patients on antipsychotics. Drug-induced hyperprolactinaemia is common and underrecognised in people on long-term antipsychotic therapy. Where sexual side effects, menstrual irregularity, or galactorrhoea arise, the preferred strategy is switching to a lower-prolactin-elevating antipsychotic (aripiprazole, quetiapine, clozapine, or olanzapine). This requires psychiatrist involvement and must not be managed unilaterally at general practice level, as antipsychotic changes carry meaningful risk in people with psychotic illness.

When to escalate

Refer or escalate when:

• Pathological hyperprolactinaemia confirmed — endocrinology for management planning and shared care
• Macroadenoma or visual symptoms — urgent endocrinology and ophthalmology; neurosurgery if mass effect is present
• Suspected pituitary apoplexy (sudden severe headache, visual loss, cranial nerve palsy) — emergency department immediately; do not wait
• Pituitary incidentaloma with hormonal abnormality or macroadenoma — endocrinology referral
• Infertility in the setting of hyperprolactinaemia — reproductive endocrinology
• Antipsychotic-induced hyperprolactinaemia requiring medication change — psychiatrist
• Failure or intolerance to all dopamine agonists
• Suspected hook effect — macroadenoma on MRI with paradoxically normal or low prolactin
• Persistent hypogonadism and bone loss despite prolactin normalisation

What this article is and is not

This is general health information drawn from current Australian clinical sources — Therapeutic Guidelines, the Australian Medicines Handbook, the RACGP, the Endocrine Society of Australia, the Australian Pituitary Foundation, and major specialist society guidelines. It is not personal medical advice and does not establish a doctor–patient relationship. Decisions about whether and how to investigate or treat elevated prolactin are made by the treating clinician who knows the individual patient.

For patient-friendly reading: HealthDirect — Prolactinoma, Better Health Channel — Pituitary gland disorders, Australian Pituitary Foundation.

---

Sources cited

1. Therapeutic Guidelines (eTG) — Hyperprolactinaemia
2. RACGP — Australian Family Physician
3. Australian Medicines Handbook — Cabergoline and bromocriptine
4. Endocrine Society of Australia
5. Australian Pituitary Foundation
6. HealthDirect — Prolactinoma
7. Better Health Channel — Pituitary gland disorders
8. TGA — PBS Authority prescribing
9. Endocrine Society 2011 — Diagnosis and treatment of hyperprolactinaemia
10. Pituitary Society 2023 — Pituitary incidentaloma consensus
11. Webster J et al. — Cabergoline vs bromocriptine (NEJM 1994)