Normal Prolactin Values in Adults
Normal serum prolactin levels in non-pregnant adults are approximately <20 μg/L (or <425 mU/L), though women typically have slightly higher baseline values than men, with upper limits around 20 μg/L in non-pregnant states. 1
Sex-Specific Reference Ranges
The normal ranges differ slightly between men and women:
- Males: 58-419 mIU/L (approximately 2.8-20 μg/L) 2
- Females: 63-561 mIU/L (approximately 3-26.5 μg/L) 2
Alternative reference ranges from population studies show:
Adult women generally have higher baseline levels than men, with typical upper limits around 20 μg/L in non-pregnant states. 1
Age-Related Variations
Prolactin levels vary throughout the lifespan:
- Highest levels occur in the first 2 years of life 1
- Lowest levels occur in mid-childhood 1
- Levels rise again during adolescence, with higher concentrations in girls than boys 1
- In older adults (>50 years), prolactin rises slightly with age in men but falls slightly in women until age 80, when it rises again 4
Clinical Interpretation Thresholds
Understanding what constitutes abnormal elevation is critical:
- 1-15 ng/mL: Corresponds to the vast majority of normal subjects (91-92.6% of normal populations) 5
- 16-20 ng/mL: Extreme limit of normal; repeat testing and follow-up recommended 5
- 21-30 ng/mL: Rare values that should be considered hyperprolactinemia requiring further investigation 5
- <100 μg/L or <2000 mU/L: Mild elevation that can occur with non-functioning pituitary adenomas, medications, stress, or other secondary causes 1
- >50 ng/mL: Suggestive of prolactinoma and warrants thorough investigation 5
Important Diagnostic Caveats
Several factors can affect prolactin measurement accuracy:
- Macroprolactinemia accounts for 10-40% of all hyperprolactinemia cases and represents biologically inactive prolactin complexes that should be excluded in cases of mild or incidental elevation 1
- Stress can elevate prolactin levels up to five times the upper limit of normal 1
- The "high-dose hook effect" causes falsely low measurements in approximately 5% of macroprolactinomas when prolactin concentrations are extremely high; manual dilution should be requested when large pituitary lesions show paradoxically normal or mildly elevated prolactin 1
- Timing is not critical for diagnosis—a single blood sample collected at any time of day is sufficient for initial assessment 6
- Specific laboratory reference ranges should always be used as values differ by assay method 1