In a 50‑year‑old woman with galactorrhea, normal CBC, CMP, thyroid‑stimulating hormone (0.93 µIU/mL) and free thyroxine (1.1 ng/dL), what is the normal total serum prolactin range and how should hyperprolactinemia be evaluated and managed?

Evaluation of Galactorrhea in a 50-Year-Old Woman

In this 50-year-old woman with galactorrhea and normal thyroid function, measure a morning fasting serum prolactin level; the normal upper limit is approximately 20 μg/L (or <425 mU/L), though laboratory-specific reference ranges should be used. 1

Normal Prolactin Reference Ranges

• Adult non-pregnant women typically have an upper limit around 20 μg/L (or <425 mU/L), though values differ by assay method and specific laboratory reference ranges must be consulted 1
• Women generally have higher baseline prolactin levels than men 1
• A single blood sample collected at any time of day is adequate for initial assessment 1

Systematic Diagnostic Approach

Initial Laboratory Evaluation

Since thyroid function is already normal (TSH 0.93, free T4 1.1), the next critical steps are:

• Measure serum prolactin in a morning fasting sample to exclude stress-related elevation 2
• If prolactin is modestly elevated (<100 μg/L or <2000 mU/L), obtain serial measurements with 2-3 samples drawn 20-60 minutes apart using an indwelling cannula to differentiate stress-related elevation from organic disease 1, 2
• Screen for macroprolactinemia if prolactin is mildly or incidentally elevated, as it accounts for 10-40% of hyperprolactinemia cases and represents biologically inactive prolactin complexes 1, 3

Medication Review

• Systematically review all medications, particularly dopamine antagonists (antipsychotics, antiemetics like prochlorperazine/Stemetil, metoclopramide), as these are among the most common causes of hyperprolactinemia 3, 2
• Medication-induced hyperprolactinemia should be excluded before pursuing further workup 1

Additional Laboratory Assessment

Although TSH is normal in this case, the complete evaluation for galactorrhea includes:

• Renal function assessment (BUN, creatinine), as chronic kidney disease causes hyperprolactinemia in 30-65% of adult patients 3, 2
• Liver function tests if severe liver disease is suspected 3

Interpretation of Prolactin Results

If Prolactin is Normal (<20 μg/L)

• Idiopathic galactorrhea with normal prolactin does not require treatment if non-bothersome 4, 5
• If bothersome, consider a short course of low-dose cabergoline (preferred dopamine agonist due to superior efficacy and tolerability) 2, 4
• Reassure the patient that this represents a benign condition 4

If Prolactin is Mildly Elevated (20-100 μg/L)

• Exclude macroprolactinemia first through secondary laboratory analysis 1, 3
• Repeat measurement to confirm persistent elevation 2
• Consider secondary causes: medications, stress, renal insufficiency 3
• If persistently elevated without clear cause, proceed to pituitary MRI 5

If Prolactin is Markedly Elevated (>100 μg/L)

• Prolactin levels generally correlate with tumor size; values >100 μg/L suggest a prolactinoma 1
• Order high-resolution pituitary MRI with and without contrast to evaluate for micro- or macroadenoma 1, 5
• If a large pituitary mass is found but prolactin seems disproportionately low (<100 μg/L), request serial dilutions to exclude the "hook effect," which occurs in approximately 5% of macroprolactinomas when extremely high prolactin saturates the immunoassay 1, 2

Management Based on Findings

If Prolactinoma is Confirmed

• Cabergoline is first-line therapy to normalize prolactin, shrink the tumor, and restore menstrual function 1
• Perform visual field testing if macroadenoma is present to assess for optic chiasm compression 6, 1
• Transsphenoidal surgery is reserved for patients who fail high-dose dopamine agonist therapy or cannot tolerate it 5

If No Adenoma and Prolactin Remains Elevated

• Re-evaluate medication list and discontinue or substitute causative agents 5
• Treat underlying conditions (hypothyroidism, renal disease) if identified 1
• Monitor prolactin levels periodically 7

Critical Pitfalls to Avoid

• Do not miss the "hook effect" in patients with large pituitary masses and paradoxically normal or mildly elevated prolactin—always request serial dilutions when clinical suspicion is high 1, 2
• Do not overlook macroprolactinemia, which is present in 10-40% of cases and does not require treatment despite elevated total prolactin 1, 3, 2
• Do not assume all galactorrhea requires treatment; normoprolactinemic idiopathic galactorrhea is benign and only needs treatment if bothersome to the patient 4, 5
• Do not forget to reassess periodically if initial workup is negative, as small tumors may be undetectable initially and grow over time 7
• Do not start dopamine agonist therapy for mild, asymptomatic hyperprolactinemia without excluding secondary causes and macroprolactinemia 1