To determine whether or not your prolactin concentrations are higher (or occasionally lower) than normal
A blood sample taken from a vein in your arm
Prolactin is a hormone produced by the anterior pituitary gland, a grape-sized organ found at the base of the brain. Prolactin concentrations are regulated by dopamine (a brain chemical), and the hormone is normally present in low amounts in men and non-pregnant women. Its main role is to promote lactation (breast milk production).
Prolactin concentrations are usually high throughout pregnancy and just after childbirth. During pregnancy prolactin, oestrogen and progesterone stimulate breast milk development. Following childbirth, prolactin helps initiate and maintain the breast milk supply. If a woman does not breastfeed, her prolactin concentration will soon drop back to pre-pregnancy levels. If she does breastfeed, suckling by the infant plays an important role in the release 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 concentrations 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 elevated prolactin concentration is a prolactinoma, a prolactin-producing tumour 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 affects 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 irregularities in menstruation; 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.
How is it used?
Prolactin concentrations are used with other test results, to help:
- Evaluate pituitary gland function (along with other hormones)
- Diagnose prolactinomas (tumours of the pituitary gland that produce prolactin)
- Monitor treatment of prolactinomas and detect recurrences
- Determine the cause of galactorrhoea
- In the investigation of the cause of headaches and visual disturbances
- In the investigation of infertility and erectile dysfunction in males
- In the investigation of infertility and irregular menstruation in females
When is it requested?
Prolactin may be requested when a patient has symptoms of a prolactinoma such as unexplained headaches, visual impairment, and/or galactorrhoea. It may also be requested, along with other tests, when a woman is experiencing infertility or irregular menses; or when a man has symptoms such as: a decreased sex drive, galactorrhoea, or infertility. Prolactin concentrations are also often requested in men as a follow-up to a low testosterone result.
When a patient has a prolactinoma, prolactin concentrations 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 concentrations may be used with other hormone test results such as growth hormone, when your doctor suspects that you have more general hypopituitarism (low levels of pituitary function which result in decreased amounts of hormones being produced). Prolactin concentrations may also be monitored when you have a condition, or are taking medications, that affects 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 results are ideally interpreted knowing when the sample is collected. Concentrations will vary over a 24 hour period - rising during sleep and peaking in the morning. Ideally, your blood sample should be taken a couple of hours after waking up, preferably after you have been resting quietly for 30 minutes (although your doctor may have reasons for doing them at other times).
High concentrations of prolactin (hyperprolactinaemia) are normal during pregnancy, and after childbirth while the mother is breastfeeding. High concentrations can also be seen with:
- Other pituitary tumours and diseases
- 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
- Anorexia nervosa
- Kidney disease
- Nipple stimulation (small increase)
- Polycystic ovary syndrome (PCOS)
- 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 drugs such as dopamine, levodopa, and ergot alkaloid derivatives.
Is there anything else I should know?
Stress from illness, trauma, work and personal problems, and even the fear of having a blood test done can cause moderate increases in prolactin concentration.
Prolactinomas are often small. Following evidence of high prolactin concentrations in your blood, your doctor may request an MRI (magnetic resonance imaging) scan of the brain to look for the presence of a tumour within the pituitary gland and, if present, to find both the size of the tumour and the size of the pituitary (which often enlarges).
What other tests may be done to evaluate an elevated prolactin?
Testosterone (concentrations will usually be low in a male when prolactin is high), FSH, and LH (to help evaluate ovulation and fertility), an MRI scan of the brain (to show pituitary enlargement and help locate a tumour), and an eye examination (to evaluate visual disturbances) may be performed. Elevated prolactin concentrations require further laboratory tests make sure that the elevation is not due to macroprolactin (see question 4).
If I have an elevated prolactin, why is my doctor testing my thyroid?
How are prolactinomas treated?
Prolactinomas are usually treated with medications that act like dopamine (such as bromocriptine or cabergoline). Treatment can reduce prolactin concentrations and symptoms and restore fertility, but the medications may have to be taken for several months or years. Surgery is sometimes necessary if the prolactinomas are large or not responding to treatment. This surgery is delicate and requires an experienced surgeon. Sometimes, despite medication and/or surgery, the prolactinoma will return.
What is macroprolactin?
Some people have an elevated prolactin concentration in their bloodstream because most of the prolactin is in a different form called macroprolactin. Macroprolactin does not come from the pituitary gland, it is not active in the body and does not indicate the presence of disease. If an elevated prolactin is found, further laboratory tests should be done to make sure that this is not due to macroprolactin.