From the Guidelines
For a 22-year-old with mildly elevated prolactin levels (30-50 ng/mL) over a 2-week period, with negative MRI, no medications, no PCOS, no nipple discharge, and not pregnant, I recommend watchful waiting with repeat prolactin testing in 3 months. This approach is based on the latest guidelines from the Nature Reviews Endocrinology 1, which suggest that a single prolactin measurement taken at any time of the day is sufficient to assess hyperprolactinaemia, but also recommend considering investigating modestly elevated serum prolactin levels by serial measurements over time to exclude the effect of stress and prolactin pulsatility. Given the mild elevation and absence of symptoms, medication treatment with dopamine agonists like cabergoline or bromocriptine is not warranted at this time. Some key points to consider in the management of this patient include:
- Ensuring the next blood sample is collected after fasting and rest for at least 30 minutes to minimize the impact of stress and other factors on prolactin levels 1
- Considering additional testing including thyroid function (TSH, free T4), renal and liver function tests, and possibly testing for macroprolactin, which is a benign form of prolactin that some lab assays detect, if levels remain elevated or increase at follow-up 1
- Being aware of the potential for the "high-dose hook effect" in prolactin assays, which can result in artificially low measurements in cases of very high prolactin concentrations, although this is less likely to be a concern in this patient with only mildly elevated prolactin levels 1
- Advising the patient that transient prolactin elevations are common and often normalize without intervention, but persistent elevation may require further investigation to rule out other causes such as medication effects, hypothyroidism, or pituitary disorders.
From the Research
Possible Causes of Hyperprolactinemia
- Hyperprolactinemia can be caused by various factors, including pituitary tumors, hypothyroidism, renal failure, cirrhosis, chest wall lesions, or idiopathic hyperprolactinemia 2, 3, 4, 5
- A prolactin-secreting pituitary adenoma (prolactinoma) is the underlying cause of hyperprolactinemia if serum prolactin levels are above 200 microg/L 2
- However, in this case, the prolactin levels are between 30 to 50, which is lower than the typical range for a prolactinoma 2
- Other possible causes of hyperprolactinemia include the intake of various drugs, compression of the pituitary stalk by other pathology, or idiopathic hyperprolactinemia 2, 3, 4, 5
Diagnostic Evaluation
- The diagnostic evaluation of hyperprolactinemia typically involves exclusion of other causes of hyperprolactinemia, such as pregnancy, primary hypothyroidism, numerous medications, and miscellaneous causes 3, 5
- A head scan, preferably an MRI, is essential to exclude a "pseudoprolactinoma" which would require surgery 3
- In this case, the MRI scan is negative, which suggests that a pituitary tumor is unlikely to be the cause of the hyperprolactinemia 2, 3
Idiopathic Hyperprolactinemia
- Idiopathic hyperprolactinemia accounts for 30-40% of cases of hyperprolactinemia 4
- The exact cause of idiopathic hyperprolactinemia is unknown, but it is thought to be related to a disruption in the normal regulation of prolactin secretion by the hypothalamus 6
- Idiopathic hyperprolactinemia can be a possible cause of the sudden increase in prolactin levels in this case, especially since the MRI scan is negative and there are no other obvious causes of hyperprolactinemia 2, 3, 4, 5
Macroprolactinemia
- Macroprolactinemia is a relatively common cause of interference in the prolactin assay that may lead to incorrect diagnosis and unnecessary investigations 6
- Macroprolactinemia can be identified by measuring prolactin post polyethylene glycol precipitation (PEG) when prolactin levels are above the reference interval 6
- It is possible that the elevated prolactin levels in this case are due to macroprolactinemia, rather than a true increase in monomeric prolactin 6