From the Guidelines
Low prolactin levels alone are not typically an indication for an MRI, as the primary concern with prolactin levels is hyperprolactinemia, which may indicate pituitary tumors or other abnormalities. According to the evaluation and management of testosterone deficiency guideline published in The Journal of Urology in 2018 1, serum prolactin should be measured in patients with low total testosterone and low or low/normal LH levels to screen for hyperprolactinemia. However, the guideline suggests that men with total testosterone levels of <150 ng/dL in combination with a low or low/normal LH should undergo a pituitary MRI regardless of prolactin levels, as non-secreting adenomas may be identified.
Key points to consider in the evaluation of low prolactin include:
- Investigating other potential causes of low prolactin, such as certain medications, hypothyroidism, or other endocrine disorders through blood tests
- Evaluating for additional symptoms suggesting pituitary dysfunction, such as visual disturbances, headaches, or abnormal levels of multiple pituitary hormones
- Considering an MRI if there are concerns about pituitary abnormalities, but this decision should be made after a complete clinical evaluation
- Focusing treatment on addressing any underlying cause rather than the low prolactin itself, as low prolactin alone rarely warrants specific treatment or advanced imaging.
From the Research
Indications for an MRI in Low Prolactin Levels
- A low prolactin level may not necessarily be an indication for an MRI, as hypoprolactinemia can be caused by various factors, including pituitary damage or dysfunction 2, 3.
- However, in cases where a pituitary tumor is suspected, an MRI may be necessary to rule out any potential issues, such as a macroprolactinoma 4.
- It's essential to note that a low prolactin level can be caused by a high-dose hook effect in the chemiluminometric assay, which can lead to falsely low prolactin levels 4.
- In patients with macroprolactinomas, regular MRI follow-up may not be necessary if prolactin levels are controlled with dopamine agonist treatment 5.
Diagnosis of Hypoprolactinemia
- Low or undetectable serum prolactin levels and the absence of a sufficient prolactin peak in the thyrotropin-releasing hormone (TRH) stimulation test are considered diagnostic for hypoprolactinemia 6.
- Basal prolactin levels of at least 5 ng/mL for males and 7 ng/mL for females can be used as cut-off levels for normal prolactin reserve 6.
- Minimum peak prolactin responses of 18 ng/mL for males and 41 ng/mL for females to TRH stimulation can exclude hypoprolactinemia 6.
Considerations for MRI
- An MRI may be necessary in cases where a pituitary tumor is suspected, or if there are any symptoms suggestive of a tumor, such as visual loss or cranial nerve palsies 4.
- However, in patients with controlled prolactin levels on dopamine agonist treatment, regular MRI follow-up may not be necessary 5.