Prolactin
Prolactin is a pituitary hormone responsible for milk production. It rises with stress, sleep and some medicines.
At a glance
- Sample
- Blood
- Units
- ng/mL (US), mIU/L (Europe)
- Often looked at with
- Testosterone, Estradiol, Cortisol
- Preparation
- Prolactin changes through the day, so blood is usually drawn 3–4 hours after waking up. Sometimes you are asked to come fasting.
Units: ng/mL and mIU/L
Labs print prolactin either as a mass, in ng/mL (common in the US), or in international units, in mIU/L (common in the UK and much of Europe); µIU/mL is the same number as mIU/L. To convert, multiply ng/mL by 21.2.
mIU/L = ng/mL × 21.2 · WHO 3rd International Standard 84/500
This converter changes units only. It doesn’t tell you whether a number is in or out of any range: that depends on the range printed by your own lab, and on your doctor. Soma does not diagnose and is not medical advice.
Why lab ranges differ
Each lab sets its reference range for its own method and analyser, and many ranges differ by age and sex. Two labs can print different ranges for the same blood, so a result is read against the range on its own report, not against a number from another lab or a website.
Soma charts every prolactin result against the range printed by the lab that measured it.
What can affect the result
- Stress or pain during the blood draw.
- Sleep: higher right after waking up.
- Breast stimulation, sex or exercise the day before.
If something like this applies, mention it to the doctor who reads your results.
Questions
How do I convert prolactin from ng/mL to mIU/L?
Multiply ng/mL by 21.2. For example, 15 ng/mL is 318 mIU/L.
Why does my lab’s prolactin range differ from another lab’s?
Each lab sets its range for its own method and equipment, and many ranges differ by age and sex. That’s why a result is best read against the range printed on the same report.
How do I prepare for a prolactin test?
Prolactin changes through the day, so blood is usually drawn 3–4 hours after waking up. Sometimes you are asked to come fasting. Follow your lab’s instructions.
Related tests
Got a lab report with Prolactin?
Share it to Soma: it reads every row on your phone, with no account and no upload, and puts your prolactin on one chart with your earlier results, each against the range your lab printed.
Sources
- Prolactin Levels — MedlinePlus, U.S. National Library of Medicine.
- Units: the factor from the WHO 3rd International Standard for prolactin, 84/500 (NIBSC).
Mention of a source doesn’t mean it endorses Soma. This page explains the test; it doesn’t diagnose and is not medical advice. Talk to your doctor about what your results mean.