Is a prolactin test usually sent out to a lab for analysis in patients presenting with symptoms suggestive of prolactin imbalance, such as galactorrhea, amenorrhea, or infertility?

Prolactin Testing: Laboratory Processing

Prolactin testing is NOT typically a send-out lab; it is a routine immunoassay performed in-house at most hospital and commercial laboratories with results available the same day or within 24 hours. 1, 2

Laboratory Logistics

• Prolactin measurement uses standard immunoassay platforms that are widely available in clinical laboratories, making it a routine test rather than a specialized send-out 1, 2
• Results are typically available within hours to one day, allowing for timely clinical decision-making in patients presenting with symptoms of hyperprolactinemia 3, 1
• A single blood sample collected at any time of day is sufficient for initial assessment, eliminating the need for specialized timing or collection procedures that might require send-out testing 3, 1

When Additional Testing May Be Required

While the basic prolactin assay is routine, certain specialized analyses may require send-out:

• Macroprolactin screening should be performed when prolactin is mildly or incidentally elevated, and this may require send-out to specialized laboratories in some institutions, as it accounts for 10-40% of hyperprolactinemia cases 1, 4, 5
• Serial dilution testing to detect the "hook effect" (occurring in ~5% of macroprolactinomas with falsely low results) may require manual processing that some laboratories send out 1, 4, 5

Clinical Context for Ordering

Prolactin should be measured in patients presenting with:

• Menstrual disturbances (amenorrhea, oligomenorrhea) in adolescent and adult women 3, 1
• Galactorrhea (inappropriate breast milk production) 3, 1, 6
• Delayed or arrested puberty in children and adolescents 3, 1
• Infertility, decreased libido, or erectile dysfunction 1, 6
• Visual field defects or headaches suggesting mass effect 3, 1

Important Caveats

• Repeat measurement is recommended for modestly elevated levels (up to 5 times the upper limit of normal) to exclude stress-related elevation, but this still uses the same in-house assay 3, 1
• Morning fasting samples are preferred for confirmation but do not change the fact that testing remains in-house 1, 2
• Before attributing hyperprolactinemia to a prolactinoma, exclude pregnancy, medications (especially dopamine antagonists), primary hypothyroidism, and renal/hepatic disease—all of which can be assessed with routine laboratory tests 1, 4, 2, 5