When to order a prolactin test?

When to Order a Prolactin Test

Prolactin testing should be ordered in patients with symptoms of hypogonadism, unexplained infertility, suspected pituitary disorders, and in men with low testosterone combined with low or low/normal luteinizing hormone levels. 1, 2

Key Indications for Prolactin Testing

Clinical Symptoms Warranting Prolactin Testing

• Order prolactin for patients presenting with symptoms of hypogonadism including:
  • In women: menstrual irregularities, amenorrhea, galactorrhea, infertility 1
  • In men: reduced sex drive, erectile dysfunction, infertility, gynecomastia 2, 1
• Test prolactin in patients with visual field changes (especially bitemporal hemianopsia) or other symptoms suggesting pituitary mass effect 2, 1
• Consider testing in patients with unexplained fatigue, reduced energy, poor concentration, or depression that could be related to hypogonadism 2

Medical Conditions Requiring Prolactin Testing

• Measure prolactin in men with low testosterone levels combined with low or low/normal luteinizing hormone (LH) levels 2, 1
• Test prolactin in patients with suspected pituitary disorders or tumors 1, 3
• Consider testing in patients with unexplained infertility 4
• Order prolactin in patients with primary hypothyroidism, as this can cause secondary hyperprolactinemia 1, 5

Diagnostic Approach for Suspected Hyperprolactinemia

Initial Testing

• Confirm hyperprolactinemia with repeat measurement, preferably in the morning while fasting 6, 1
• For modestly elevated prolactin levels, consider serial measurements with samples taken 20-60 minutes apart using an indwelling cannula 6, 1
• Always measure luteinizing hormone (LH) levels in patients with confirmed hyperprolactinemia to help establish etiology 2, 1

Ruling Out Secondary Causes

• Review medications that can cause hyperprolactinemia, particularly antipsychotics and other dopamine antagonists 1, 5
• Screen for pregnancy, primary hypothyroidism, liver disease, and renal failure before pursuing further workup 1, 5
• Assess for macroprolactinemia in patients with mildly elevated prolactin levels, especially if asymptomatic 6, 1

Follow-up Testing and Management

When to Refer to Endocrinology

• Refer patients with persistently elevated prolactin levels of unknown etiology for further evaluation 2, 1
• Men with total testosterone <150 ng/dL combined with low/low-normal LH should be referred regardless of prolactin levels 2, 1

Treatment Considerations

• Dopamine agonists (cabergoline preferred over bromocriptine) are the first-line treatment for prolactinomas and hyperprolactinemia 6, 7, 8
• Monitor prolactin levels 1-3 months after initiating treatment and every 3-6 months until stabilized 6

Pitfalls to Avoid

• Do not miss the "hook effect" - falsely low prolactin levels in large tumors due to assay saturation 1, 5
• Do not overlook macroprolactinemia - present in 10-40% of patients with hyperprolactinemia and may not require treatment 1, 5
• Avoid using screening questionnaires as a substitute for laboratory testing of testosterone and prolactin 2
• Do not forget to obtain pituitary MRI when prolactin levels are significantly elevated or when patients have symptoms of mass effect 1, 3