Serum prolactin refers to the level of prolactin hormone present in the blood. This polypeptide hormone is produced by lactotroph cells located in the anterior pituitary gland, a small endocrine gland situated at the base of the brain. Prolactin plays a role in various bodily processes.
Prolactin’s Core Functions
Prolactin is primarily synthesized in the anterior pituitary gland. Its most recognized function is stimulating milk production, known as lactogenesis, in the mammary glands during pregnancy and maintaining lactation during breastfeeding. The number of lactotroph cells in the pituitary gland increases during pregnancy to support the physiological demand for breast tissue development and milk production. Beyond its role in lactation, prolactin influences reproductive health in both men and women. It plays a part in regulating menstrual cycles in women and impacts sperm production in men. Prolactin also has an inhibitory effect on the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which can affect the release of hormones necessary for menstruation and fertility.
Understanding Prolactin Levels
Serum prolactin levels are measured through a simple blood test, which can be ordered by a doctor. These reasons include investigating infertility, irregular menstrual cycles, unexpected milk production (galactorrhea), or when a pituitary issue is suspected.
Normal prolactin levels can vary depending on individual factors such as gender, time of day, and physiological states like pregnancy or breastfeeding. To prepare for a prolactin test, individuals are often advised to fast and have the blood drawn at a specific time, usually in the morning.
In non-pregnant, non-breastfeeding adults, normal serum prolactin levels are generally less than 25-30 μg/L, though specific reference ranges may differ slightly between laboratories. For males, typical ranges are around 2 to 18 ng/mL, while for females, they are usually 2 to 30 ng/mL.
Causes and Symptoms of High Prolactin
Elevated serum prolactin levels, a condition known as hyperprolactinemia, can stem from various causes. The most common pathological cause is a prolactinoma, which is a benign tumor of the pituitary gland that produces prolactin. These tumors are more frequently observed in females.
Certain medications are also known to elevate prolactin levels. These include some antipsychotics, antidepressants, certain blood pressure medications, and opioids. Other medical conditions can contribute to hyperprolactinemia, such as an underactive thyroid (hypothyroidism), kidney disease, liver disease, and irritation to the chest wall. Additionally, physiological factors like stress, intense exercise, sleep, and nipple stimulation can temporarily increase prolactin concentrations.
The symptoms of high prolactin levels differ between sexes. In women, hyperprolactinemia can lead to menstrual irregularities, difficulty conceiving, galactorrhea (breast milk production unrelated to pregnancy or breastfeeding), reduced libido, and vaginal dryness. For men, symptoms include decreased libido, erectile dysfunction, gynecomastia (enlargement of breast tissue), galactorrhea, and infertility. When high prolactin is caused by a pituitary tumor, individuals might also experience headaches or changes in vision due to the tumor pressing on nearby structures.
Addressing Abnormal Prolactin Levels
Diagnosing abnormal prolactin levels typically begins with the blood test, but further diagnostic steps may be necessary to determine the underlying cause. If a pituitary tumor is suspected, a magnetic resonance imaging (MRI) scan of the pituitary gland is often performed. Other hormone tests, such as thyroid function tests, may also be conducted to rule out other medical conditions.
For hyperprolactinemia, the primary treatment usually involves medications called dopamine agonists, such as cabergoline or bromocriptine. These medications work by mimicking the action of dopamine, which naturally inhibits prolactin secretion from the pituitary gland, thereby helping to reduce prolactin levels and often shrink prolactinomas. Surgery may be considered if medications are ineffective, if the tumor is large and causing vision impairment, or if a patient cannot tolerate the medication. Radiation therapy is a less common treatment option, typically reserved for specific cases where other treatments have not been successful.
In cases of low prolactin (hypoprolactinemia), which is less common, causes can include damage to the pituitary gland or Sheehan’s syndrome. Symptoms often involve difficulty with breastfeeding after delivery. Treatment for low prolactin is generally not required unless it specifically impacts breastfeeding, as other functions of prolactin are less commonly affected to a degree requiring intervention.