Hormones
High Prolactin Levels: What a Raised Result Actually Means
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20266 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.
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UK laboratories act on a prolactin above 700 mIU/L, not on anything above the printed range. That figure is an action threshold rather than a red line. Before anyone investigates, the lab checks a first raised sample for macroprolactin, an inactive form that fools the test. Stress at the needle raises it too.
Not sure which markers you need? Build your test →Prolactin came back high. You searched it, found the word pituitary in the first result, and your evening changed. That is the usual route to this page.
So here is the calmer version, in the order a UK laboratory actually works through it. Prolactin is the hormone that drives milk production. Everyone makes some, and plenty of ordinary things push it up.
1. What counts as a high prolactin in the UK?
UK reports print prolactin in mIU/L. Some labs write mU/L, which is the same unit. The clinical biochemistry department at the Royal United Hospitals Bath sets the bar plainly for GPs: “Prolactin > 700 mIU/L on a single sample without excessive venepuncture stress, at any time of day in both males and females is considered clinically significant hyperprolactinaemia and requires further investigation.”
The same guidance adds the line that saves a lot of worry. The 700 figure “is a clinical action threshold and not a reference range”. So a result of 520 can sit above your report’s printed range and still be nowhere near the point of action.
Our normal prolactin levels guide covers the everyday range for men and women.
2. Find your own number
Most people arrive holding one value. Here is how UK laboratory guidance groups it. The right-hand column describes what happens next, not what is wrong with you.
| Your result | Band | Usual next step |
|---|---|---|
| Under 700 mIU/L | Below the action line | Discuss only if you have symptoms. |
| 700 to 2,000 mIU/L | Mild | Repeat in 4 weeks, avoiding stress at sampling. |
| 2,000 to 5,000 mIU/L | Significant | Prompt repeat and referral to endocrinology. |
| Above 5,000 mIU/L | Severe | Urgent endocrinology referral. |
Notice that the mild band, which is where most raised results land, leads to a repeat rather than a referral. In men, symptoms worth mentioning include low libido, difficulty with erections and breast tissue changes. Our gynaecomastia guide covers that last one.
3. The lab artefact ruled out before anything else
This is the single most useful thing to know, and almost nobody is told it. Prolactin can travel around the body stuck to an antibody. That bundled form is called macroprolactin. It is biologically inactive, so it does nothing at all, but it still registers on the test and inflates your result.
UK laboratories know this and check for it. The Bath guidance says the lab “will routinely screen for macroprolactin on every first raised (>700 IU/L) prolactin seen in an individual patient”. Published estimates put macroprolactin in roughly 10 to 25 in every 100 people with a raised prolactin.
Put differently. Before your result means anything about hormones, there is a real chance it means something about the assay. That check happens without you asking for it.
4. What pushes prolactin up?
Three groups, and the first two are far more common than the third.
Everyday causes. Stress counts, including the stress of the needle itself. So do exercise, sleep, a recent meal, pregnancy and breastfeeding. Bath advises repeating after two to three days rested when exercise is the likely reason.
Medicines. A long list raises prolactin. Antipsychotics are the best known. Antidepressants including the SSRIs, anti-sickness drugs such as metoclopramide and domperidone, verapamil, methyldopa, omeprazole, trimethoprim and high-dose oestrogens all appear on the Bath list. If you take any of these, say so before anyone investigates further.
Medical causes. An underactive thyroid raises prolactin, which is why thyroid function is checked alongside. Kidney and liver disease can too, as can PCOS and pituitary conditions. That last group is what a specialist is for.
The thyroid link is worth acting on. If your prolactin is raised, check whether TSH was measured in the same set. Our normal thyroid levels guide covers what that number means.
5. What happens next
For a mild result, the pathway is unhurried and it is mostly about getting a cleaner second sample.
- The lab excludes macroprolactin on the first raised sample.
- Thyroid function is checked, and pregnancy is excluded.
- Your medicines are reviewed against the known list.
- A repeat is taken at about four weeks, rested and unstressed.
- If nothing explains it, your GP refers you to endocrinology.
If stress at the needle is the suspected reason, Bath suggests a sample drawn through a cannula after 30 minutes of rest. That is a GP or clinic request, not something a home test can do.
6. Which blood test measures prolactin?
Helvy’s Complete Male Hormones panel (£119) reports prolactin alongside testosterone, free testosterone, SHBG, LH, FSH, DHEA-S and albumin. Reading prolactin next to LH and testosterone is the point, because a raised prolactin tends to pull testosterone down with it.
It is a home finger-prick test, processed by UKAS-accredited UK labs. It measures your prolactin. It does not investigate a raised one, and it does not replace the laboratory macroprolactin check or a GP review.
Not sure which fits? The build-my-test tool walks you through it, and the men’s hormones hub covers what else sits in the picture.
READY TO TEST?
See prolactin with the hormones around it
Helvy’s home blood tests report prolactin with testosterone, LH, FSH and SHBG, each explained in words you already use, so one figure never sits there on its own. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What prolactin level is considered high in the UK?
UK laboratory guidance acts on a prolactin above 700 mIU/L on a single sample taken without excessive stress at the needle. That figure is a clinical action threshold rather than a reference range, so a result slightly above your printed range is not the same thing.
Can stress cause a high prolactin result?
Yes, including the stress of the blood draw itself. Exercise, sleep, a recent meal and a seizure within the last few hours all raise it too. If exercise is the likely reason, UK guidance suggests repeating after two to three days rested.
What is macroprolactin?
It is prolactin bound to an antibody. The bundle is biologically inactive, so it does nothing in your body, but it still registers on the assay and inflates the result. UK labs screen for it on every first raised prolactin above 700.
Which medicines raise prolactin?
Antipsychotics are the best known. The list also includes antidepressants and the SSRIs, metoclopramide and domperidone, verapamil, methyldopa, omeprazole, trimethoprim and high-dose oestrogens. Tell your GP everything you take before further investigation.
Does a high prolactin always mean a pituitary problem?
No. Stress, medicines, an underactive thyroid, kidney or liver disease and the macroprolactin artefact all raise it. A pituitary cause is one item on a long list, and it is what an endocrinology referral is for.
Does high prolactin lower testosterone?
It can. Raised prolactin suppresses the signals that drive testosterone production, which is why a low testosterone reading is sometimes investigated with a prolactin test. Reading the two together says more than either alone.