Hormones
Prolactine
Pituitary hormone for milk production; raised by stress, medicines or a benign pituitary tumor.
Everything about this testWhat it measures
Prolactin is made in the pituitary gland and drives milk production after childbirth. Outside pregnancy and breastfeeding the value is low, because the brain substance dopamine inhibits its release. Too high a prolactin suppresses the signals to the ovaries and testes, resulting in absent periods, less interest in sex or erection problems. The value rises temporarily with stress, pain, sleep, after a meal and after breast stimulation.
- Hyperprolactinemia (too much prolactin) as the cause of absent or irregular periods, infertility, milk discharge, less interest in sex or erection problems
- Prolactinoma: a benign tumor of the pituitary gland that makes prolactin
- Side effect of medicines that block dopamine (antipsychotics, some antidepressants and medicines for nausea)
- Reduced function of the pituitary gland (low prolactin, rare)
High
A slightly raised prolactin is often due to stress around the blood draw, lack of sleep, a meal, breast stimulation or intensive exercise, and is usually normal when repeated. Other common causes are medicines that block dopamine (antipsychotics, metoclopramide, domperidone, some antidepressants), estrogens, an underactive thyroid, reduced kidney function, pregnancy and breastfeeding. With a very high value, a prolactinoma is likely: a benign tumor of the pituitary gland that is usually small in women and more often large in men, sometimes with headache or loss of part of the visual field. Symptoms that go with a raised prolactin: absent or irregular periods, milk discharge, less interest in sex, erection problems, infertility and, in the long term, bone loss. Some of the 'raised' results are due to macroprolactin, a harmless bound form that the laboratory can check separately.
Low
A low prolactin usually has no meaning and causes no symptoms. It fits the use of dopamine-like medicines (including cabergoline, bromocriptine and levodopa) or, rarely, reduced function of the pituitary gland as a whole. After childbirth, a low prolactin can go together with a lack of milk production.
Preparation
- Have your blood taken in the morning, at least 1 hour after getting up.
- Take it easy: stress and heavy exercise shortly before the sample is taken raise prolactin.
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
The GP repeats a raised value at rest and fasting, looks at medicines, pregnancy, thyroid and kidney function, and has macroprolactin checked if needed. With a repeatedly clearly raised value, referral to an internist-endocrinologist follows, usually with an MRI of the pituitary gland.
Reliability
A single slightly raised value proves nothing, because prolactin reacts strongly to stress, food and medicines; a repeat test at rest, fasting and at least an hour after getting up is the first step. The level of the value does say something: the higher it is, the greater the chance of a prolactinoma. According to the Dutch GP guideline (NHG) on amenorrhea, prolactin is mainly meaningful with milk discharge, headache or visual field symptoms, and with absent periods lasting longer than a year without explanation.
Limitations
- Stress and pain around the blood draw, a meal, breast or nipple stimulation, sex and intensive exercise shortly before temporarily raise the value; a blood draw at rest, fasting and at least an hour after getting up is the most reliable.
- Medicines: antipsychotics, metoclopramide, domperidone, some antidepressants, estrogens and opioids raise prolactin; dopamine agonists and levodopa lower it.
- An underactive thyroid and reduced kidney function raise prolactin; a raised value is therefore often assessed together with TSH and creatinine.
- Macroprolactin (a harmless bound form) gives a falsely raised result; with a raised value without symptoms, the laboratory can check for this.
How common is this
A slightly raised prolactin is a common, usually harmless finding. A prolactinoma is rarer: in the Netherlands the diagnosis is made in about 500 to 700 people a year, mainly in women between 20 and 40. It is, however, the most common hormone-producing tumor of the pituitary gland.
Who is this useful for
Useful with absent or irregular periods without explanation, with milk discharge outside breastfeeding, with infertility, in men with repeatedly low testosterone or erection problems with less interest in sex, and with headache with visual field symptoms. Also when taking antipsychotics with symptoms that fit a high prolactin. In people without these symptoms, the result says little; a chance finding of a slightly raised value often leads to unnecessary further tests.
Downsides and risks
- A slightly raised value due to stress or medicines can wrongly lead to fear of a brain tumor and to an unnecessary MRI.
- An MRI after a slightly raised value sometimes finds a small, harmless pituitary abnormality that has nothing to do with the symptoms but does lead to years of check-ups.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results