What is Prolactin?
Prolactin is a hormone produced by the pituitary gland, a pea-sized gland located at the base of the brain. This hormone is strongly associated with lactation. When a woman is breastfeeding, production of this hormone stimulates the breasts to fill with milk.
In addition, prolactin is involved in the suppression of the sex hormones estrogen and testosterone. This is why women who are lactating do not have menstrual periods, as estrogen is essential in regulating the menstrual cycle.
Prolactin is also involved in the production of cells called oligodendrocyte precursors. These cells mature into oligodendrocytes, which are important in nerve function.
Normally, prolactin levels are low in both men and women. Levels of this hormone are high only when a woman is pregnant or breastfeeding.
Certain diseases can cause abnormal increase or decrease in prolactin levels.
The Prolactin Blood Test
Someone might undergo a prolactin blood test for several different reasons. High prolactin levels can occur in kidney disease, polycystic ovary syndrome, and diseases of the hypothalamus region of the brain. In addition a test might be ordered for many other reasons.
- To confirm a pregnancy
- To determine the cause of lactation issues. For example, some people experience a condition called galactorrhea, where lactation occurs in the absence of pregnancy.
- Certain types of sexual dysfunction in men are linked to an increase in prolactin levels.
- Hypothyroidism (low-functioning thyroid gland) can lead to increased levels of prolactin.
- In some women, infertility can be caused by increased prolactin levels, as high levels of this hormone can prevent ovulation and menstrual periods.
- Excess amounts of dopamine can cause prolactin levels to rise.
- Diagnosis of prolactinoma, a benign pituitary gland tumor that can cause increased prolactin production.
- Certain prescription medications, including certain types of anti-psychotics and hypertension drugs, can cause a rise in prolactin.
Like most blood tests, the prolactin blood test is a simple procedure. To perform this test the healthcare worker cleans the inside of the elbow with an antiseptic. This is the most common site for blood to be drawn; alternatively blood might be drawn from a site on the back of the hand.
The healthcare worker then wraps an elastic band around the upper arm to fill the inner elbow vein with blood and make needle insertion easier. Once the needle has been inserted, the elastic band is removed to allow blood to be drawn. In most cases only a mild stinging sensation is felt; in rare cases the injection might cause moderate pain.
This blood test is often ordered with other tests such as those for follicle-stimulating hormone, luteinizing hormone, testosterone, estrogen, and progesterone. These tests are part of the diagnostic process for infertility causes in both men and women.
If thyroid disease is suspected, the prolactin blood test might be ordered in conjunction with blood tests to check thyroid function.
Interpretation of Prolactin Test Results
Results of the prolactin blood test must be interpreted with certain factors in mind. The main factor is that prolactin levels can vary considerably during the course of the day. For most people, levels of this hormone are at their highest in the morning. Therefore, doctors generally recommend their patients take the test within a couple of hours after they wake up.
Normal blood prolactin levels are very low.
For men, the normal range is 2 to 18 ng/ml (nanograms per milliliter)
For non-pregnant women, the normal range is 2 to 29 ng/ml.
In pregnant or breastfeeding women, the normal level range is 10 to 209 ng/ml.
In women who are not pregnant or breastfeeding, and in men, an increased level of prolactin is commonly caused by one of the following:
- Hypothalamus disease
- Kidney disease
- Thyroid disease causing hypothyroidism
- Pituitary tumor
- Chest wall trauma
Lab Tests Online: The Prolactin Test
National Institute of Health MedlinePlus: Prolactin
NIH Endocrine and Metabolic Diseases Information Service: Prolactinoma