From the Guidelines
A workup for borderline high prolactin (hyperprolactinemia) levels should begin with assessing baseline macroprolactin levels to distinguish between monomeric prolactin and macroprolactin, as recommended by the consensus guideline for the diagnosis and management of pituitary adenomas in childhood and adolescence 1. When evaluating borderline high prolactin levels, it's essential to consider the potential presence of macroprolactin, which has low biological activity and may not require treatment. The initial investigation should include prompt and appropriate secondary analysis to detect the possible presence of macroprolactin. Key points to consider in the workup include:
- Assessing baseline macroprolactin levels to distinguish between monomeric prolactin and macroprolactin
- Evaluating for symptoms such as galactorrhoea, oligo-amenorrhoea, and pituitary adenomas
- Considering the presence of macroprolactinaemia, which can be present in 10-40% of individuals with hyperprolactinaemia
- Reviewing the patient's medical history to identify potential causes of hyperprolactinemia, such as pituitary disorders or medications
- Laboratory tests, such as thyroid function tests and comprehensive metabolic panel, may be warranted to rule out other potential causes of symptoms
- Imaging studies, such as MRI of the pituitary, may be necessary if other pituitary hormones are abnormal or if symptoms suggest pituitary dysfunction, as recommended by the consensus guideline 1.
From the Research
Diagnosis of Borderline Low Prolactin Levels
The diagnosis of borderline low prolactin levels, also known as hypoprolactinemia, can be challenging. According to 2, a basal PRL level of ≤ 5.7 ng/ml in males and 7.11 ng/ml in females was 100% specific in predicting an inadequate response to TRH stimulation test with 80% and 70% sensitivity respectively.
TRH Stimulation Test
The TRH stimulation test is used to evaluate the prolactin reserve. As stated in 3, a minimum peak prolactin response of 18 ng/mL for males and 41 ng/mL for females to TRH stimulation can exclude hypoprolactinemia. However, larger population studies across different age groups and sexes are needed to better define normal basal prolactin levels and prolactin responses to the TRH stimulation test.
Key Findings
Some key findings related to the diagnosis of hypoprolactinemia include:
- 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 3
- Hypoprolactinemia can serve as a marker for extensive pituitary gland damage and dysfunction 3
- Dopamine agonist-induced hypoprolactinemia can impair sexual functioning and well-being in young women 4
Clinical Implications
In clinical practice, the diagnosis of hypoprolactinemia is important because it can be associated with metabolic dysfunctions, fertility problems, and sexual dysfunction. As noted in 5, hypoprolactinemia in patients with polycystic ovary syndrome (PCOS) may contribute to metabolic alterations such as insulin resistance, obesity, and diabetes mellitus.
Evaluation of Prolactin Levels
The evaluation of prolactin levels should take into account the gender of the patient, as well as the presence of any underlying medical conditions. According to 6, the prevalence of TSH and ACTH deficiency in men with macroprolactinomas was 41% and 23%, respectively. In addition, recovery of thyrotroph function occurred in 4/9 cases, and recovery of corticotroph function occurred in 4/6 cases 6.