How is hyperprolactinemia diagnosed?

A blood test can be done to check prolactin levels. A prolactin level of 20 to 25 nanograms per milliliter (ng/ml) is considered normal. A level of up to 50 ng/ml may be a normal fluctuation. With a prolactinoma, the level usually exceeds 250 ng/ml. A diagnosis of hyperprolactinemia requires two tests that both show a clearly elevated prolactin level.^[1]

It is important to remember that prolactin levels fluctuate throughout the day and are higher in the afternoon than in the morning. The blood sample should be taken while fasting and about 2 hours after waking in the morning. In the case of a slightly elevated prolactin level, the sample should be repeated. Some conditions that may cause elevated prolactin levels are seizures or trauma, excessive exercise, and certain medications, such as antipsychotics (e.g., risperidone), antidepressants (e.g., paroxetine), and antihypertensives (e.g., verapamil).^[2]

If a prolactinoma is suspected as the cause of hyperprolactinemia, an MRI scan is the preferred imaging modality to look for the tumor.^[1]