Prolactin
At a Glance
Why Get Tested?
To determine whether or not your prolactin levels are higher (or occasionally lower) than normal
When to Get Tested?
When you have symptoms of an elevated prolactin, such as galactorrhoea and/or visual disturbances and headaches, as part of investigation for female and male infertility, and for investigation of low testosterone in men
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
The Test Sample
What is being tested?
Prolactin is a hormone produced by the pituitary gland, a grape-sized organ found at the base of the brain. Normally present in low amounts in men and non-pregnant women, prolactin's main role is to promote lactation (breast milk production).
Prolactin levels are usually high throughout pregnancy and just after childbirth. During pregnancy prolactin, oestrogen and progesterone stimulate breast development. Following childbirth, prolactin helps initiate and maintain the breast milk supply. If a woman does not breastfeed, her prolactin soon drops back to low pre-pregnancy levels. If she does breastfeed, suckling by the infant plays an important role in the production of prolactin. When the baby feeds, this has an effect on the amount of prolactin secreted by the pituitary, and this is turn controls the amount of milk produced. Prolactin levels will continue to be high while the mother continues to breastfeed, but will eventually fall back to pre-pregnancy levels.
Besides pregnancy, the most common cause of raised prolactin levels are certain prescribed medications and prolactinomas; prolactin-producing tumours of the pituitary gland. Prolactinomas are the most common type of pituitary tumour and are usually benign. They develop more frequently in women but are also found in men.
Problems can arise both from the unintended effects of excess prolactin, such as milk production in the non-pregnant woman (and rarely, man) and from the size and location of the tumour. If the pituitary gland and/or the tumour enlarge significantly it can put pressure on the optic nerve, causing headaches and visual disturbances; and it can interfere with the other hormones that the pituitary gland produces.
In women, prolactinomas can cause infertility and irregular periods; in men, these tumours can cause a gradual loss in sexual function and desire. If left untreated, prolactinomas may eventually damage tissues surrounding them.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
How is it used?
Prolactin levels are used with other tests, to help:
- Determine the cause of galactorrhoea
- Determine the cause of headaches and visual disturbances
- Diagnose infertility and erectile dysfunction in males
- Diagnose infertility in females
- Diagnose prolactinomas (tumours of the pituitary gland that produce prolactin)
- Evaluate pituitary gland function (along with other hormones)
- Monitor treatment of prolactinomas and detect recurrences
When is it requested?
Prolactin levels may be used when a patient has symptoms of a prolactinoma such as unexplained headaches, visual impairment and/or galactorrhoea. They may also be used, along with other tests, when a woman is experiencing infertility or irregular periods; or when a man has symptoms such as: a decreased sex drive, galactorrhoea or infertility. Prolactin levels are also often ordered in men as a follow-up to a low testosterone level.
When a patient has a prolactinoma, prolactin levels may be used to monitor the growth of the tumour and its response to treatment. They may also be used at regular intervals to monitor for prolactinoma recurrence.
Prolactin levels may be used with other hormone levels such as growth hormone, when your doctor suspects that you have more general hypopituitarism (low levels of pituitary function which result in lowered levels of hormones being produced). Prolactin levels may also be monitored when you have a condition or are taking medications that affect dopamine (a brain chemical that controls the production of prolactin).
What does the test result mean?
Men and non-pregnant women will normally have only small amounts of prolactin in their blood. The levels are ideally interpreted knowing when the sample was collected. The levels will vary over a 24 hour period - rising during sleep and peaking in the morning. Ideally, your blood sample should usually be taken a couple of hours after waking up, preferably after you have been resting quietly for 30 minutes (although your doctor may have his or her own reasons for doing them at other times).
High levels of prolactin (hyperprolactinaemia) are normal during pregnancy and after childbirth while the mother is breastfeeding. High levels can also be seen with:
- Drugs: Oestrogen, tricyclic antidepressants, and drugs that block the effect of dopamine (a brain chemical that controls the production of prolactin) such as tranquilizers, some hypertension drugs, and some drugs that are used to treat gastro-oesophageal reflux
- Hypothalamic diseases
- Hypothyroidism
- Kidney disease
- Nipple stimulation (small increase)
- Other pituitary tumours and diseases
- Polycystic ovary syndrome (PCOS)
- Prolactinomas
- Macroprolactinaemia.
Levels of prolactin that are below normal are not usually treated but may be indicative of a more general hypopituitarism (decreased pituitary function and decreased hormone production). Low levels may also be caused by some drugs.
Is there anything else I should know?
Stress from illness, trauma, work and personal problems, and even the fear of having the blood test done can cause moderate increases in prolactin.
Prolactinomas are often small. Your doctor may request an MRI (magnetic resonance imaging) scan to help locate the tumour within the pituitary gland and to look at both the size of the tumour and the size of the pituitary (which often enlarges).
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
