Prolactin test: what the result means (PRL)

Prolactin is a hormone made by the pituitary gland, a gland in the brain. Its main function is to stimulate milk production after birth, so during pregnancy and while breastfeeding prolactin levels are naturally high. In non-pregnant women and in men, prolactin is usually low. Prolactin also rises during sleep, after physical exertion, stress or a meal, which is why a resting state is recommended for the test.

Prolactin is tested together with other pituitary and sex hormones when a pituitary lesion, a disturbed menstrual cycle, infertility or male sexual dysfunction is suspected. The most common cause of a raised prolactin level is a benign pituitary tumour called a prolactinoma; it can be identified and treated effectively if it is diagnosed in time.

• In women, when the menstrual cycle becomes irregular or stops altogether without pregnancy
• When milk or fluid leaks from the breasts without pregnancy or breastfeeding (galactorrhoea)
• When a woman is unable to conceive (looking for the causes of infertility)
• In men, when erections become difficult, sex drive falls or the breasts enlarge (gynaecomastia)
• When a pituitary tumour is suspected, or to monitor the treatment of a prolactinoma that is already known
• In men, when facial or body hair decreases without a clear reason

A raised prolactin level is most often linked to a prolactinoma — a benign pituitary tumour — and also to hypothyroidism, kidney disease, an injury to the chest wall or certain medicines. MedlinePlus notes that cannabis use can raise prolactin as well. The cause is established by assessing the symptoms, other hormones and, if needed, pituitary imaging.

• A prolactinoma — a benign pituitary tumour (the most common cause)
• Hypothyroidism (reduced thyroid function)
• Kidney disease
• An injury to the chest wall or the nipple, nipple piercings
• Some antidepressants, oestrogen preparations, anti-nausea or antipsychotic medicines, and also cannabis use
• Other pituitary lesions or diseases of the hypothalamus

Symptoms that can go with a raised prolactin level

• Milk or fluid leaking from the breasts without pregnancy or breastfeeding (galactorrhoea)
• Irregular or absent periods, infertility
• In men — erectile problems, reduced sex drive, breast enlargement (gynaecomastia)

What to discuss with a doctor

• Whether the symptoms match galactorrhoea, menstrual disturbances or erectile problems — worth discussing with a doctor
• Whether you take medicines that can raise prolactin (for example certain antidepressants or anti-nausea medicines)
• Assessment of thyroid function (TSH) and of kidney indicators
• Pituitary imaging (MRI), if a prolactinoma is suspected

A low prolactin level is rare. According to MedlinePlus, a low prolactin level can indicate a pituitary disorder — the pituitary may then also fail to make enough of its other hormones. Because it is rare, such a result is always worth discussing with a doctor together with other pituitary indicators.

• Pituitary insufficiency (hypopituitarism) — the pituitary does not make enough hormones
• Some medicines that reduce prolactin production

What is usually assessed after a low result

• Assessment of other pituitary hormones (for example TSH, cortisol), if a general pituitary disorder is suspected
• A conversation with a doctor about symptoms linked to a hormone deficiency
• Pituitary imaging, if the cause needs clarifying

Units, repeat tests and related pages

Lithuanian laboratories often report prolactin in mU/l rather than µg/l, and the conversion factor depends on the particular assay system, so the exact interval should be read from your own report. A single raised result is usually repeated and assessed together with other tests, and the doctor chooses the exact panel according to the symptoms. Related pages: TSH, FSH, LH, oestradiol, testosterone, progesterone, and how to read blood test results.