Understanding Hyperprolactinaemia: Causes, Diagnosis, and Treatment

Hyperprolactinaemia, characterized by elevated levels of prolactin in the blood, is a condition that can have various underlying causes. While mildly elevated prolactin levels (ranging from 500 to 2000 mU/L or approximately 25 to 100 ng/mL) may prompt the need for further investigation, it is essential to consider multiple differential diagnoses. This condition is often recognized in women experiencing amenorrhoea, and in some cases, galactorrhoea.

When prolactin levels are modestly increased, several factors could be at play. Pregnancy is a common physiological cause, but other conditions like primary hypothyroidism can also lead to elevated prolactin due to increased thyrotropin-releasing hormone (TRH) stimulation. Additionally, stress, certain medications—such as dopamine receptor antagonists and antihypertensives—chronic renal failure, and even idiopathic reasons can elevate prolactin levels.

In clinical practice, confirming hyperprolactinaemia typically involves conducting multiple stress-free blood tests. If prolactin levels exceed 3000 mU/L (about 150 ng/mL), a microprolactinoma, a benign pituitary tumor, may be suspected. If levels are particularly high, over 6000 mU/L (approximately 300 ng/mL), a macroprolactinoma could be present.

The diagnosis of hyperprolactinaemia requires a comprehensive approach. Alongside measuring serum prolactin, evaluating thyroid function, renal health, and conducting pregnancy tests are vital steps. A thorough medication history is also crucial, as certain drugs can inhibit dopamine action or synthesis, leading to increased prolactin production and possibly resulting in galactorrhoea.

Most commonly, a microprolactinoma is the source of elevated prolactin levels, especially in women of reproductive age. However, in cases of larger macroprolactinomas, it’s important to assess other anterior pituitary hormone axes, as they may also be affected. Sometimes, the presence of acromegaly may also be considered, as some pituitary tumors can secrete both growth hormone and prolactin.

Treatment for hyperprolactinaemia often involves the use of dopamine agonists, such as cabergoline, which can effectively lower prolactin levels. Surgical intervention or radiotherapy is rarely required but may be necessary in specific cases. Understanding the myriad causes of hyperprolactinaemia is crucial for appropriate diagnosis and management, ensuring that patients receive the best possible care.