Prolactin levels are used, along with other tests, to help:

• Determine the cause of galactorrhea
• Determine the cause of headaches and visual disturbances
• Diagnose infertility and erectile dysfunction in males
• Diagnose infertility in females
• Diagnose prolactinomas
• Evaluate anterior pituitary function (along with other hormones)
• Monitor treatment of prolactinomas and detect recurrences

Prolactin levels may be ordered when a patient has symptoms of a prolactinoma such as: unexplained headaches, visual impairment, and/or galactorrhea. They may also be ordered, 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, galactorrhea, 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 ordered to monitor the progress of the tumor and its response to treatment. They may also be used at regular intervals to monitor for prolactinoma recurrence.

Prolactin levels may be ordered, along with other hormone levels such as growth hormone, when your doctor suspects that you have more general hypopituitarism (low levels of pituitary function that result in lowered levels of thyroid or adrenal hormones). And prolactin levels may be monitored when you have a condition or are taking medications that may affect dopamine (a brain chemical that regulates and inhibits the production of prolactin).

Men and non-pregnant women will normally have only small amounts of prolactin in their blood. Prolactin levels do, however, need to be evaluated based on the time of day that they are 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 drawn a couple of hours after waking up, preferably after you have been resting quietly for 30 minutes (although your doctor may have his own reasons for doing them at other times).

High levels of prolactin (hyperprolactinemia) are normal during pregnancy and after childbirth while the mother is nursing. High levels are also seen with:

• Anorexia nervosa
• Drugs: Estrogen, tricyclic antidepressants, and drugs that block the effect of dopamine (a brain chemical that regulates and inhibits the production of prolactin) such as: tranquilizers, some hypertension drugs, and some drugs that are used to treat gastroesophageal reflux
• Hypothalamic diseases
• Hypothyroidism
• Kidney disease
• Nipple stimulation (moderate increase)
• Other pituitary tumors and diseases
• Polycystic ovary syndrome
• Prolactinomas

Levels of prolactin that are below normal are not usually treated but may be indicative of a more general hypopituitarism. Low levels may also be caused by drugs such as: dopamine, levodopa, and ergot alkaloid derivatives.

Stresses from illness, trauma, and even the fear of having the blood test done can cause moderate increases in prolactin.

Prolactinomas are often small. Along with prolactin levels, your doctor may do an MRI (magnetic resonance imaging) of the brain, both to try and locate the tumor within the pituitary gland and to look at both the size of the tumor and the size of the pituitary (which often enlarges).