What is prolactin?

Prolactin is a hormone secreted by the pituitary gland. It is involved in lactation, breast development, and other physiological processes.

What is a healthy prolactin level?

Different laboratories may vary with regards to the reference ranges used for prolactin, but the following ranges provide a rough guide:

• Healthy: <600mIU/l
• Modestly raised: 600–3000mIU/l
• Raised: 3000–6000mIU/l
• High: >6000mIU/l

Although <600mIU/l is classified as the “healthy” range, it is important to note that prolactin levels of 600–3000mIU/l within the “modestly raised” range can be healthy and do not necessarily indicate an underlying disease process. This is because prolactin levels can be influenced by a variety of factors, such as stress and exercise. This is a vital point to understand, as prolactin levels within the “modestly raised” range do not necessarily warrant immediate alarm or intervention.

What causes prolactin levels to rise?

Prolactin levels of 600–3000mIU/l within the “modestly raised” range can be due to a wide range of factors, including stress, exercise, nipple stimulation, chest binding, and pregnancy.

Some drugs can also cause prolactin levels to rise. These include antipsychotics (especially risperidone), antidepressants, and anti-nausea medication (such as domperidone and metoclopramide).

Less commonly, there are some medical conditions which can raise prolactin levels to the “modestly raised” range. These include polycystic ovarian syndrome, hypothyroidism, and kidney disease.

Much more rarely, prolactin levels within the “raised” and “high” levels may be caused by a prolactinoma. This is a usually benign tumour of the pituitary gland that secretes prolactin. However, a prolactinoma is usually associated with prolactin levels >3000mIU/l. If your prolactin level is <3000mIU/l, then you are very unlikely to have a prolactinoma.

What are the symptoms of a prolactinoma?

Symptoms associated with prolactinoma are neurological and include visual disturbances, headaches, dizziness, loss of balance, nausea, and vomiting. These occur when the tumour reaches a significant size.

Also, as noted above, a prolactinoma is usually associated with prolactin levels >3000mIU/l. Hence, if your prolactin level is <3000mIU/l and you have none of the above neurological symptoms, then it is very unlikely that you have a prolactinoma.

Can gender affirming hormone treatment cause prolactinoma?

No. There is no evidence that gender affirming hormone treatment causes prolactinoma. People who are receiving gender affirming hormone treatment are no more likely to develop a prolactinoma than people who are not receiving gender affirming hormone treatment.

How will gender affirming hormone treatment affect my prolactin levels?

Feminising hormone treatment with oestrogen can raise prolactin levels. The antiandrogen cyproterone acetate can also sometimes slightly raise prolactin levels. However, the raised prolactin levels due to feminising hormone treatment usually remain within the “modestly raised” range of 600–3000mIU/l and do not cause any clinically significant problems. Therefore, there is no need for routine checking of prolactin levels for people who are receiving gender affirming hormone treatment.

As noted above, there is no evidence that gender affirming hormone treatment causes prolactinoma. Therefore, there is no special need for people receiving gender affirming hormone treatment to screen for prolactinoma, unless there are specific clinical indications such as neurological symptoms.

When should I check my prolactin level?

As noted above, there is no need for routine checking of prolactin levels in people receiving gender affirming hormone treatment.

If you have neurological symptoms, such as visual disturbances, headaches, dizziness, loss of balance, nausea, and vomiting, then you are strongly recommended to seek medical attention from your doctor. Your doctor will perform an examination and may include a prolactin level as part of the investigations to arrive at a diagnosis.

What do I do if I have had a blood test for prolactin and it shows that my prolactin level is raised?

If your prolactin level is >3000mIU/l or you have neurological symptoms suggestive of a prolactinoma, then it is recommended that you seek medical attention urgently with your doctor. Your doctor can then undertake a neurological examination and arrange further tests, such as a scan of the head, to investigate for a prolactinoma.

If your prolactin level is 1000–3000mIU/l, then it is unlikely that you have a prolactinoma. Nonetheless, you are advised to see your doctor on a routine basis to investigate other potential causes of the modestly raised prolactin. This might include checking your thyroid and reviewing your medication history. Often, there may be no underlying medical cause, as prolactin can be modestly raised due to factors such as stress, exercise, and nipple stimulation.

If your prolactin level is <1000mIU/l and you have no symptoms, then no further action or monitoring is required.