Prolactin Test

The Prolactin test, also called the serum prolactin level test, measures the level of prolactin hormone in your blood. Prolactin is a hormone produced by the pituitary gland, a small gland located at the base of the brain. Its primary role is to stimulate and maintain breast milk production (lactation) after childbirth. In women who are not pregnant or breastfeeding, prolactin levels are normally low. In men, prolactin is present in small amounts and plays a role in reproductive function.

Doctors order a Prolactin test because abnormally high prolactin levels (hyperprolactinaemia) disrupt the hormonal balance of the reproductive system - suppressing ovulation in women and reducing testosterone in men. The most common cause of significantly elevated prolactin is a prolactinoma - a benign (non-cancerous) tumour of the pituitary gland that secretes excess prolactin. When detected early, prolactinomas are highly treatable with oral medication.

The Prolactin test monitors the pituitary gland's hormonal output and its impact on the reproductive system. It is used to evaluate irregular menstrual periods, unexplained infertility, abnormal milk discharge (galactorrhoea), erectile dysfunction in men, and to monitor prolactinoma treatment. Fasting is recommended for the most accurate result. Suitable for both men and women.

A Prolactin test is performed when symptoms of abnormal prolactin levels are present or when a pituitary tumour is suspected based on clinical evaluation.

This test is usually recommended for:

• Women with irregular, infrequent, or absent menstrual periods (oligomenorrhoea or amenorrhoea) without a clear cause.
• Women experiencing unexplained infertility or difficulty conceiving - high prolactin suppresses ovulation.
• Anyone with galactorrhoea - unexpected milk discharge from the breasts in women who are not pregnant or breastfeeding, or from the breasts in men.
• Men with reduced libido, erectile dysfunction, infertility, or an unexplained decrease in testosterone levels.
• Men or women with persistent headaches or visual disturbances, which may indicate a pituitary tumour pressing on surrounding structures.
• Patients already diagnosed with a prolactinoma - for monitoring treatment effectiveness with dopamine agonist therapy.
• Patients on medications known to raise prolactin - including antipsychotics (haloperidol, risperidone), metoclopramide, and domperidone.

Prolactin testing frequency depends on whether you are being tested for the first time, whether you have a confirmed prolactinoma, and how well treatment is working.

A Prolactin test is primarily used to diagnose and evaluate conditions associated with abnormal prolactin levels, including:

• Prolactinoma - a benign pituitary tumour that overproduces prolactin. The most common pituitary tumour. Microprolactinomas (less than 10 mm) cause hormonal symptoms; macroprolactinomas (more than 10 mm) can also cause headaches and visual disturbances.
• Hyperprolactinaemia - the clinical syndrome of abnormally high prolactin from any cause, leading to menstrual irregularity, infertility, and galactorrhoea in women, and hypogonadism in men.
• Hypothyroidism - elevated TSH in hypothyroidism stimulates the pituitary to produce more prolactin. Treating hypothyroidism alone can normalise prolactin.
• Drug-Induced Hyperprolactinaemia - many medications, including antipsychotics, antiemetics, and some antihypertensives, raise prolactin as a side effect.
• Hypopituitarism - a poorly functioning pituitary gland can produce abnormally low prolactin, detected by a less-than-normal result.
• Polycystic Ovary Syndrome (PCOS) - mild prolactin elevation is sometimes found alongside PCOS, contributing to menstrual irregularity and infertility.

Important Note: A single elevated prolactin result does not confirm a prolactinoma. Stress, exercise, and food can transiently raise prolactin. Repeat testing under ideal conditions is always required before a diagnosis is made.

What to Expect Before the Prolactin Test

Fasting for 8 to 12 hours before the test is recommended for the most accurate result. The test should ideally be collected in the morning, 3 to 4 hours after waking, as prolactin peaks during sleep and early morning hours. Avoid vigorous physical exercise, recent sexual activity, and breast stimulation for at least 2 hours before the test - all of which can temporarily raise prolactin. Inform your doctor about all current medications, especially antipsychotics, antiemetics, and metoclopramide.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein - you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Prolactin Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and relax for a few minutes. Your digital report will be available within 24 hours.

The Prolactin test measures a single key parameter:

• Serum Prolactin Level - Measured in ng/mL (nanograms per millilitre) or mIU/L (milli-international units per litre). This is the primary result your doctor uses to assess pituitary function and its impact on the reproductive system. Normal values differ significantly between men, non-pregnant women, pregnant women, and breastfeeding women. The result must always be interpreted alongside these population-specific reference ranges.

Because prolactin secretion is pulsatile (released in bursts), a single reading can be misleading. Stress, physical activity, food, breast stimulation, sleep, and even the act of blood collection itself can temporarily raise prolactin. For this reason, a significantly elevated result is typically confirmed with a repeat fasting morning sample before a diagnosis of hyperprolactinaemia is made.

Prolactin normal values vary significantly between population groups. The table below shows standard reference ranges.

Important Note: Normal prolactin ranges vary between laboratories and assay methods.

The prolactin result must always be interpreted in the context of your gender, pregnancy status, symptoms, and current medications.

Disclaimer: This table is for educational purposes only. Prolactin interpretation requires the expertise of a qualified endocrinologist or gynaecologist. A single elevated result must be repeated before clinical decisions are made.

Potential Risks and Complications

The Prolactin test is a very safe, routine blood test. Complications are extremely rare, and most people feel only a brief pinch. Consult a doctor if: 

• The puncture site does not stop bleeding after gentle pressure
• You notice unusual redness, swelling, warmth, or lasting pain at the needle site
• You feel persistently lightheaded after the blood draw - sit and rest for a few minutes.

Understanding Prolactin Test Limitations

Prolactin is highly sensitive to physical and emotional stressors; even the anxiety of a blood draw can temporarily raise levels. A single elevated result is therefore insufficient for diagnosis and must be confirmed with a repeat morning fasting sample. Macroprolactin (biologically inactive prolactin aggregates) can cause falsely elevated total prolactin without true hyperprolactinaemia, a macroprolactin screening test may be needed. Medications including antipsychotics, metoclopramide, and domperidone are common causes of elevated prolactin that can be missed without a thorough medication review. Low prolactin requires evaluation of the full pituitary hormone panel.

An elevated prolactin is the starting point of a pituitary and hormonal investigation. Your doctor will recommend the following tests depending on the degree of elevation and clinical presentation.

Note: Treatment for hyperprolactinaemia, typically with dopamine agonists such as cabergoline or bromocriptine, is highly effective in reducing prolactin levels and shrinking prolactinomas. Always consult an endocrinologist before starting or adjusting treatment.

Pro Tip: Book your Prolactin test on PharmEasy - a certified phlebotomist will come to your doorstep, and your digital report will be delivered within 24 hours. Convenient, affordable, and accurate.