The pituitary gland is in the base of the brain and produces prolactin. At times, prolactinoma, a tumor develops in the gland that leads to excessive production of prolactin. Depending on the size and the position of the tumor, it may put pressure on the optic nerve leading to headaches and interferes with vision. These tumors are benign and causes excess prolactin to be released in the blood; symptoms of which includes unexplained nipple discharge in non-pregnant women and decreased libido and infertility in men.

Reference Values
Reference value for Prolactin is as below

• Normal level in Males: 2 to 18 nanograms per milliliter (ng/mL)
• Normal levels in Nonpregnant females: 2 to 29 ng/mL.
• Normal levels in Pregnant females: 10 to 209 ng/mL.

Interpretations
Men and non-pregnant women will normally be present with 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 show 24-hour variation, rising during sleep and at its peak in the morning. Ideally, a person's blood sample for prolactin testing should be drawn after 3 to 4 hours after waking up as prolactin levels tend to fluctuate during sleep and after waking up.
Hyperprolactinemia or high level of prolactin is seen during pregnancy and in breastfeeding mothers. Prolactin promotes lactation and prolactin levels drop after the mother stops breastfeeding.

A high level may also be seen with:

• Tumors that produce and release prolactin (prolactinomas)
• The eating disorder anorexia nervosa
• Diseases of the hypothalamus
• Hypothyroidism
• Kidney disease
• Liver disease
• Polycystic ovary syndrome
• Other pituitary diseases and tumors