Hyperprolactinaemia is the presence of abnormally high levels of prolactin in the blood. Normal levels average to about 13 ng/mL in women, and 5 ng/mL in men, with an upper normal limit of serum prolactin levels being 15-25 ng/mL for both. When the fasting levels of prolactin in blood exceed this upper limit,  hyperprolactinemia is indicated. Prolactin (PRL) is a peptide hormone produced by lactotroph cells in the anterior pituitary gland. PRL is involved in lactation after pregnancy and plays a vital role in breast development. Hyperprolactinemia may cause galactorrhea (production and spontaneous flow of breast milk), infertility, and disruptions in the normal menstrual period in women; as well as hypogonadism, infertility and erectile dysfunction in men. Although hyperprolactinemia can result from normal physiological changes during pregnancy and breastfeeding, it can also be caused by other etiologies. For example, high prolactin levels could result from diseases affecting the hypothalamus and pituitary gland. Other organs, such as the liver and kidneys, could affect prolactin clearance and consequently, prolactin levels in the serum. The disruption of prolactin regulation could also be attributed to external sources such as medications.In the general population, the prevalence of hyperprolactinemia is 0.4%. The prevalence increases to as high as 17% in women with reproductive diseases, such as polycystic ovary syndrome. In cases of tumor-related hyperprolactinemia, prolactinoma is the most common culprit of consistently high levels of prolactin as well as the most common type of pituitary tumor. For non-tumor related hyperprolactinemia, the most common cause is medication-induced prolactin secretion.
Unlike women, men do not experience reliable indicators of elevated prolactin such as menstruation to prompt immediate medical consultation. As a result, the early signs of hyperprolactinemia are generally more difficult to detect and may go unnoticed until more severe symptoms are present. For instance, symptoms such as loss of libido and sexual dysfunction are subtle, arise gradually, and may falsely indicate a differential cause. Many men with pituitary tumor-associated hyperprolactinemia may forego clinical help until they begin to experience serious endocrine and vision complications, such as major headaches or eye problems.Long-term hyperprolactinaemia can lead to detrimental changes in bone metabolism as a result of hypoestrogenism and hypoandrogenism. Studies have shown that chronically elevated prolactin levels lead to increased bone resorption and suppression of bone formation, leading to reduced bone density, increased risk of fractures, and increased risk of osteoporosis. The chronic presence of hyperprolactinemia can lead to hypogonadism and osteolysis in men. Causes
Prolactin secretion is regulated by both stimulatory and inhibitory mechanisms. Dopamine acts on pituitary lactotroph D2 receptors to inhibit prolactin secretion while other peptides and hormones, such as thyrotropin releasing hormone (TRH), stimulate prolactin secretion. As a result, hyperprolactinemia may be caused by disinhibition (e.g., compression of the pituitary stalk or reduced dopamine levels) or excess production. The most common cause of hyperprolactinemia is prolactinoma (a type of pituitary adenoma). A blood serum prolactin level of 1000–5000 mIU/L (47-235 ng/mL) may arise from either mechanism, however levels >5000 mIU/L (>235 ng/mL) is likely due to the activity of an adenoma.