Prolactin is the hormone that tells the body to make breast milk when a person is pregnant or breast-feeding. Production of prolactin takes place in the pituitary gland.
For most men and women who are not pregnant or breast-feeding, there are only low levels of prolactin in the body. Doctors measure the hormone levels in nanograms per milliliter (ng/mL).
Normal levels are:
A prolactin level test is simple and measures the amount of the hormone in the blood. It can check to see if levels are too low or too high.
When should prolactin levels be measured?
A blood test can measure prolactin levels.
Doctors will measure prolactin levels to obtain more information about someone's health.
They may check levels of other hormones at the same time. This information can help explain the cause of specific medical concerns.
A doctor may recommend a prolactin level test if someone:
- produces breast milk when not pregnant or breast-feeding
- has symptoms of a growth on the pituitary gland called a prolactinoma
- has another pituitary disorder
- experiences infertility or irregular periods
- has a medical condition that affects how much dopamine they make
What is the procedure?
A technician will take a small blood sample from a vein in a person's arm. They will then send the sample for testing.
The natural levels of prolactin in the body change throughout the day. Levels gradually rise overnight and are at their highest in the morning.
Doctors usually ask to take a blood sample 3 to 4 hours after a person has woken up.
What do the results mean?
A disorder of the pituitary gland may cause high prolactin levels.
Usually, it is not necessary to treat low levels of prolactin.
A common cause of low levels is medication. Some examples include dopamine and levodopa. In some cases, low levels of prolactin may be a sign of a pituitary disorder, for example, hypopituitarism.
This is a rare condition that can delay growth and puberty in children, and cause premature aging in adults.
Prolactin levels of between 30 ng/mL and 200 ng/mL are considered moderately high. This level of prolactin in the blood can have many causes.
Conditions related to raised levels of prolactin include:
- pituitary disorders
- polycystic ovary syndrome (PCOS)
- kidney disease
- liver disease
- anorexia nervosa
If test results show high levels of prolactin, further tests may be needed.
If a doctor suspects that a prolactinoma is causing high levels, they may recommend a CT or MRI scan.
The scan can look at the pituitary gland and show if there is a growth and how large it has become. Doctors can then decide what action and treatment to recommend.
A prolactinoma will usually remain small in females. It often does not cause other health problems, although it will affect hormone levels.
A prolactinoma can be large in men. The growth may put pressure on the nerves between the brain and the eye. This can cause problems with vision and headaches.
How do prolactin levels affect fertility?
For women, high levels of prolactin in the blood can stop the ovaries from making the hormone estrogen.
Low levels of estrogen can cause irregular periods or stop periods completely, reduce sex drive, and cause vaginal dryness. A person may also find it more challenging to get pregnant.
For men, high levels of prolactin can cause erectile dysfunction and low sex drive.
This effect in men is because prolactin can stop the testes from producing the hormone testosterone. In some cases, it may cause infertility, but this is rare.
Treatment for high prolactin levels
Medication is the standard treatment for high prolactin.
High prolactin levels are normal during pregnancy and while someone is breast-feeding. Some medical conditions may raise levels including:
Some medications can cause high prolactin levels, including:
- some antidepressants
- drugs containing estrogen, such as birth control pills
- medication used to treat hypertension
- some medications used to treat acid reflux
Marijuana use can also cause prolactin levels to rise.
A doctor will usually ask about medical history and any drugs a person is taking before they do a prolactin level test.
Treatment for high levels is usually with medication, normally Parlodel or Dostinex.
If someone has a prolactinoma, medication can usually reduce the size of the tumor.
The medication used to treat high levels can cause side effects, such as nausea and stomach issues. Doctors will only gradually increase the amount of medication they prescribe to a person for this reason.
Surgery may be used to treat small tumors. Tumors are usually smaller in females than in males and are often easier to remove.
Surgery may also sometimes be recommended if medication has not been successful.
Insurance and cost
Hormone testing is not classed as an essential health benefit, so there is no legal requirement for an insurance plan to cover it. But every insurance plan is different, and many will cover a prolactin level test.
Raised levels of prolactin may indicate an underlying health condition. Higher levels are normal in pregnant women and those who are breast-feeding.
The test to measure prolactin levels is simple and can help doctors to prescribe the correct medication to reduce levels or provide treatment for an underlying condition that may be causing the raised levels.