Prolactin: what it is, what it tells you and when it’s tested

Prolactin is a hormone made by the pituitary, a small gland at the base of the brain. Its main job is to make milk after giving birth. Men have it too. If it is too high, it holds back ovulation in women and testosterone in men.

When it’s tested

In women, doctors order it when periods are irregular or missing, when milk comes from the nipple without breastfeeding, or when a pregnancy does not come. In men, when there is low sex drive, erection problems or low testosterone.

It is not a routine test for people who feel well. It rises for many harmless reasons, such as the stress of the blood test, and a high result without symptoms often leads to needless tests.

That is why Rosa does not test it. Instead it looks at two things that often raise it: your thyroid, through TSH, and your kidneys, through creatinine and eGFR.

What it tells you, and what it does not

If it is high, your doctor looks for why. Often it is a medicine, stress or the thyroid. Sometimes it is a small benign growth on the pituitary, a prolactinoma.

Sometimes it is high only on paper: the blood holds a large, inactive form, macroprolactin, which causes no symptoms. One extra test picks it up.

If it is normal, the pituitary is usually not behind your symptoms.

That is why it is read together with other tests:

• TSH: An underactive thyroid can raise it
• Creatinine: If your kidneys work less well, it rises
• Testosterone: A high prolactin lowers it
• LH: It shows whether the pituitary signals the ovaries and testicles

Normal prolactin levels

The lab decides what is normal, and in women the upper limit is usually higher than in men. Many reports use ng/mL, others µIU/mL, with much larger numbers: always check the unit.

In pregnancy and while breastfeeding, prolactin is high, and that is normal.

The stress of the blood test raises it. That is why some labs have you rest first, or take several samples a little apart. Follow their instructions.

If your prolactin is high or low

• High prolactin: Often a medicine, stress or the thyroid. Sometimes a benign pituitary growth, usually treated with medicines.
• Low prolactin: Usually not a problem. Rarely, after giving birth, it can make breastfeeding hard.

What can skew the result

A few things raise it for a short while, without any disease. It helps to know them before your blood test.

• The stress of the test: Anxiety, waiting, a difficult draw all raise it. Arrive calm and rest for a few minutes.
• Sleep: It rises during the night. A test just after waking can give a higher result.
• Your breasts: Stimulating the nipple, even with a breast examination, raises it for a while.
• Some medicines: Antipsychotics, some antidepressants, anti-sickness medicines such as metoclopramide and domperidone. Tell your doctor, and do not stop them on your own.

When to worry

Talk to your doctor if:

• Your periods are irregular or have stopped for months, and you are not pregnant.
• Milk comes from your nipple and you are not breastfeeding.
• You are a man with low sex drive, erection problems or growing breasts.
• Your prolactin is above the range on your report on a second test.
• You have headaches that do not go away or you see less at the sides: see your doctor soon.

Frequently asked questions

What are normal prolactin levels? They depend on the lab and your sex: in women the upper limit is usually higher. The range on your own report counts, and the unit it uses.

What does prolactin do? Mostly it makes milk after giving birth. If it is too high, it holds back ovulation and periods in women, and testosterone in men.

Do I need to fast for a prolactin test? Follow your lab’s instructions. They often ask for fasting and a few minutes of rest before the draw, because stress raises it.

Does stress raise prolactin? Yes, even just the stress of the blood test. That is why a slightly high result is repeated, at rest, before any other tests.

Does Rosa test prolactin? No. Rosa measures TSH, creatinine and eGFR, which say a lot about two common causes of high prolactin. If your doctor wants prolactin, they order it separately.

Sources

• Melmed and colleagues, diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2011. PMID 21296991
• Petersenn and colleagues, diagnosis and management of prolactin-secreting pituitary adenomas: a Pituitary Society international consensus statement. Nature Reviews Endocrinology, 2023. PMID 37670148