Levels and units
Normal prolactin levels are usually:
Women: <440mIU/L (<25ng/mL)
Men: <350mIU/L (<20ng/mL)
These maximum levels vary slightly due to different standards. The level of prolactin also vary during the day and is highest during sleep. The schedule below shows prolactin level means calculated on the basis of ‘n’ people:
|Proband||Prolactin, ng/mL||Prolactin, mIU/L|
|Women, follicular phase (n=803)||12.1||257|
|Women, luteal phase (n=699)||13.9||295|
|Women, mid cycle (n=53)||17||360|
|Women, whole cycle (n=1555)||13.0||276|
|Women, pregnant 1st trimester (n=39)||16||339|
|Women, pregnant 2nd trimester (n=52)||49||1039|
|Women, pregnant 3rd trimester (n=54)||113||2396|
|Men, 21-30 (n=50)||9.2||195|
|Men, 31-40 (n=50)||7.1||151|
|Men, 41-50 (n=50)||7.0||148|
|Men, 51-60 (n=50)||6.2||131|
|Men, 61-70 (n=50)||6.9||146|
On this website I use the unit mIU/L if nothing else is stated.
Two main units are used when measuring prolactin levels. These are mIU/L and ng/mL. The factor between them is 21.2.
- ng/mL = nano-grams per mili-liter
- mcg/L= µg/L = micro-grams per liter
- mIU/L = mili-international-units per liter
ng/mL = mcg/L = µg/L
The conversion factor from mass to units is 21.2.
(ng/mL) x 21.2 = mIU/L
Example: 15ng/mL x 21.2 = 318mIU/L
The unit mUI/L refers to an international standard (IS) called ‘IS 84/500’.