Hormones
Normal Prolactin Levels: Reading a UK Number
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed August 20265 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
QUICK ANSWER
UK labs report prolactin in mU/L. North West London Pathology reads men under 310 mU/L and women under 420 mU/L as normal, and Leeds Teaching Hospitals treats anything up to 700 mU/L as normal. A mildly raised first result is usually repeated before anything else happens.
Not sure which markers you need? Build your test →Your prolactin comes back at 480. You search it, and every chart you find says normal is under 25. So you spend an evening convinced something is badly wrong.
It almost certainly is not. Those charts are American and they use a different unit. Once you convert, 480 becomes about 23. This guide covers the UK ranges, the unit trap, and why one raised reading is rarely the end of the story.
1. What is a normal prolactin level in the UK?
Prolactin is the pituitary hormone behind milk production. The pituitary is a pea-sized gland under your brain. Everyone makes prolactin, and the ranges differ by sex.
| Lab | Men | Women |
|---|---|---|
| North West London | under 310 | under 420 |
| Royal Cornwall | 73 to 407 | 109 to 557 |
The gap between those two labs is the first useful lesson. Ranges are set by the assay each lab runs, so a result that is high at one lab can be normal at another. Leeds Teaching Hospitals pathology publishes a simpler working line: up to 700 mU/L is normal, and up to 1000 mU/L is worth repeating.
Read your number against the range printed on your own report. That is the only range that was actually used to produce it.
2. Why UK numbers look nothing like the charts online
UK labs report prolactin in milli-international units per litre, or mU/L. American labs report nanograms per millilitre, or ng/mL. The two differ by a factor of about 21.
- To go from mU/L to ng/mL, divide by 21.2.
- To go from ng/mL to mU/L, multiply by 21.2.
- So 480 mU/L is roughly 23 ng/mL.
This single conversion resolves most late-night panics about prolactin. If a chart quotes a normal ceiling around 20 or 25, it is almost certainly in ng/mL.
3. Why a mildly raised result gets repeated
Two reasons, and both are common enough to expect.
The first is the needle. Prolactin rises with stress, including the stress of having blood taken. A nervous draw can lift a normal person over the line, which is why a single mildly raised value is usually checked again on a calmer day.
The second is macroprolactin. Some of your prolactin clumps together with an antibody into a large complex that the body cannot use, but the analyser still counts.
“a polymeric form of prolactin in which several molecules form aggregates with circulating IgG”
— North West London Pathology, macroprolactin investigations
NHS labs handle this automatically. North West London runs the macroprolactin check whenever a man reads above 450 mU/L or a woman above 600 mU/L. Royal Cornwall runs it above 700 mU/L. The follow-up result tells your GP how much of the total is the active form.
4. What pushes prolactin up
Beyond the sample itself, these are the usual explanations:
- Pregnancy and breastfeeding, where a high level is the point.
- Medication, especially some antipsychotics, antidepressants and anti-sickness drugs.
- An underactive thyroid, which nudges prolactin up as a knock-on effect.
- Chest wall irritation or recent nipple stimulation.
- A benign growth on the pituitary, which is what a clinician investigates once the simple causes are ruled out.
In men, a persistently raised prolactin can quietly lower testosterone, which is why the two get read together. If low drive or flat energy is what brought you here, our low libido blood test guide covers the wider marker set.
5. Which blood test reports your prolactin
The marker is prolactin, reported in mU/L. Helvy's Complete Male Hormones panel (£119) reports it alongside testosterone, free testosterone, SHBG, LH, FSH, DHEA-S and albumin. Reading prolactin next to testosterone is the whole reason it is in there.
One honest boundary. Complete Male Hormones is the only Helvy panel that carries this marker, so it is the one to check if prolactin is specifically what you want measured.
Sample in the morning, and stay off the needle-day coffee run if you can. Our prolactin blood test guide covers preparation in more detail, and the build-my-test tool helps you pick markers.
READY TO TEST?
See your prolactin next to the hormones it moves
Helvy's home blood tests report prolactin in UK units with plain-English context, read beside testosterone rather than on its own. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What is a normal prolactin level in mU/L?
North West London Pathology reads men under 310 mU/L and women under 420 mU/L as normal. Royal Cornwall publishes 73 to 407 for men and 109 to 557 for women. Leeds treats up to 700 mU/L as normal. Use your own report.
How do I convert prolactin from mU/L to ng/mL?
Divide by 21.2. A UK result of 480 mU/L is about 23 ng/mL. Going the other way, multiply ng/mL by 21.2. Most charts quoting a ceiling near 20 or 25 are using ng/mL.
Is a prolactin of 500 mU/L high?
It sits above the North West London ceiling for both sexes and inside the Royal Cornwall range for women. Leeds would call it normal. That spread is exactly why a single mildly raised value is repeated rather than acted on.
Can stress raise your prolactin?
Yes, including the stress of the blood draw itself. It is a well-recognised cause of a mildly raised reading, and it is one of the reasons a repeat sample on a calmer day is the standard next step.
What is macroprolactin?
North West London Pathology describes it as a polymeric form of prolactin in which several molecules form aggregates with circulating IgG. The clumps are inactive but still get counted, so labs run a separate check on raised samples.
Does high prolactin lower testosterone?
A persistently raised prolactin can suppress the signals that drive testosterone production, which is why the two markers are read together. One raised prolactin reading on its own does not establish that.
Related guides
Prolactin Blood Test UK
What the marker does, and how to prepare for an accurate result.
Testosterone Levels by Age
The hormone prolactin can quietly hold down.
DHEA-S Levels by Age UK
The adrenal hormone read in the same panel.
Normal Thyroid Levels UK
An underactive thyroid nudges prolactin up.
Gynaecomastia Blood Test UK
The markers checked when breast tissue changes in men.
Blood Test Reference Ranges UK
Why normal on a lab report is a population range, not a target.