?A raised prolactin blood test does not automatically mean there is a problem with your pituitary gland.
Prolactin is a hormone that can change in response to pregnancy, breastfeeding, stress, strenuous exercise, certain medicines and other physiological factors. Even the stress associated with having blood taken can temporarily increase the result.
Persistently high prolactin levels, however, can interfere with reproductive hormone signalling and may sometimes indicate an underlying hormonal, thyroid, kidney or pituitary issue that needs further investigation.
The important question is therefore not simply whether prolactin is above the laboratory range. It is whether the elevation is persistent, how high it is, whether relevant symptoms are present and whether another explanation can account for it.
For people who specifically need the hormone checked, London Blood Tests offers a private Prolactin Blood Test with clinic and home blood collection options.
What Is a Prolactin Blood Test?
Prolactin is a peptide hormone produced primarily by the anterior pituitary gland, a small endocrine gland located at the base of the brain.
It is best known for its role in breast development and milk production, but prolactin also interacts with the reproductive hormone system in women and men.
A prolactin blood test measures the concentration of prolactin circulating in the blood.
You may also see the investigation described as a serum prolactin test, PRL blood test or simply a prolactin test. These terms generally refer to measurement of the same hormone.
Prolactin testing may form part of an investigation into menstrual irregularities, fertility problems, unexplained breast milk production, low testosterone, reduced libido, erectile dysfunction or suspected pituitary dysfunction.
The result is most useful when it is interpreted in the context of why the test was requested.
What Do High Prolactin Levels Mean?
A persistently raised prolactin concentration is known as hyperprolactinaemia.
A laboratory result above the reference range tells you that prolactin was elevated in that particular blood sample.
It does not tell you why.
Pregnancy and breastfeeding naturally increase prolactin. Stress, exercise and some medicines can also cause temporary elevations.
Other causes can include hypothyroidism, reduced kidney function and disorders affecting the hypothalamus or pituitary gland.
This creates an important distinction:
One raised prolactin result is not necessarily the same as persistent hyperprolactinaemia.
When an unexpected elevation is found, the circumstances surrounding the sample and the wider clinical picture can be as important as the initial number.
Why Can Prolactin Rise Temporarily?
Prolactin is responsive to both physical and psychological stimuli.
Stress is a recognised example. Travelling to an appointment, waiting for blood collection or feeling anxious about venepuncture may contribute to a temporary rise in some people.
Strenuous exercise can also increase prolactin, as can breast or nipple stimulation.
Prolactin secretion also changes during sleep and across the day.
For these reasons, a modest unexpected elevation may sometimes be repeated under more controlled conditions before extensive investigations are considered.
The purpose of repeating the test is not to ignore the original abnormal result. It is to establish whether the elevation remains present when avoidable influences have been reduced.
What Can Cause Persistently High Prolactin?
Several different mechanisms can produce sustained hyperprolactinaemia.
Pregnancy and Breastfeeding
Prolactin naturally increases during pregnancy and lactation because the hormone supports milk production.
Pregnancy status therefore needs to be considered when interpreting an elevated result in someone who could be pregnant.
Medicines
Some medicines can increase prolactin because of their effects on dopamine.
Dopamine normally suppresses prolactin secretion. Medicines that interfere with dopamine signalling can therefore allow prolactin concentrations to rise.
Certain antipsychotic medicines are particularly well recognised for this effect, although other medicines may also contribute.
A prescribed medicine should not be stopped simply because prolactin is elevated. Medication changes need to be discussed with the clinician responsible for the treatment.
Underactive Thyroid
Hypothyroidism can contribute to raised prolactin.
Thyroid function may therefore be considered when unexplained hyperprolactinaemia is being investigated.
This is a good example of why an elevated prolactin result does not automatically lead directly to pituitary imaging. Sometimes the explanation lies elsewhere in the endocrine system.
Kidney Function
Reduced kidney function can affect prolactin clearance and may contribute to increased concentrations.
Kidney markers may therefore be relevant in selected cases.
Pituitary Conditions
The pituitary produces prolactin, so conditions affecting this gland can alter the hormone's concentration.
A prolactinoma is a benign prolactin-secreting pituitary tumour.
However, a raised prolactin blood test does not automatically mean that a prolactinoma is present. The degree of elevation, symptoms, medication history, repeat results and other hormone findings all influence whether specialist pituitary investigation is required.
Does High Prolactin Mean You Have a Pituitary Tumour?
No.
A prolactinoma is one recognised cause of persistent hyperprolactinaemia, but there are many other explanations.
Pregnancy, breastfeeding, medicines, hypothyroidism, kidney disease, physiological stress and other pituitary conditions may all affect the result.
Instead of interpreting an isolated value as evidence of a tumour, a more useful sequence of questions is:
Was the result only mildly raised?
Could stress, exercise or sample conditions have affected it?
Are any medicines known to raise prolactin being taken?
Is thyroid function normal?
Are symptoms present?
Does prolactin remain elevated when reassessed?
Only after that context is established does it become possible to decide whether broader pituitary investigation is warranted.
What Is Macroprolactin?
Macroprolactin is an important but less widely understood part of prolactin testing.
Most biologically active prolactin circulates as relatively small hormone molecules. Sometimes prolactin binds to an immunoglobulin, creating a much larger molecular complex known as macroprolactin.
Routine laboratory prolactin assays may detect this form.
Macroprolactin has much less biological activity than ordinary monomeric prolactin, so total prolactin can sometimes appear high even though the biologically active portion is less elevated. This is known as macroprolactinaemia.
Some UK laboratories automatically investigate macroprolactin when the total prolactin result exceeds their specified threshold.
Identifying it matters because it can help distinguish true biologically active hyperprolactinaemia from an apparent laboratory elevation caused predominantly by macroprolactin.
In other words, the headline prolactin result may not always tell the complete story.
What Happens After a High Prolactin Result?
What happens next depends on how elevated the result is, whether symptoms are present and whether there is already a plausible explanation.
Mildly Raised Prolactin
A modest elevation may sometimes be repeated, particularly when stress, exercise or the circumstances of sample collection could have influenced the result.
The purpose is to determine whether prolactin remains elevated.
Possible Medication-Related Elevation
Medication history should be reviewed carefully.
Where a medicine is a possible cause, the result can be discussed with the clinician responsible for prescribing it.
Do not stop an antipsychotic, antidepressant or other prescribed medicine solely because prolactin is elevated.
Raised Prolactin With Menstrual or Fertility Problems
A broader reproductive hormone assessment may provide more useful information than prolactin alone.
The London Blood Tests Fertility Hormones Profile measures prolactin together with FSH, LH and oestradiol, helping place the result within the wider reproductive hormone pathway.
Raised Prolactin With Low Testosterone or Male Hormonal Symptoms
Prolactin may need to be considered alongside testosterone, LH, FSH and SHBG.
The Male Hormone Profile includes prolactin with testosterone and other markers involved in androgen and pituitary-reproductive function.
If low testosterone is also being investigated, our guide to the best time for a testosterone blood test in London explains why sample timing, repeat testing, LH, FSH and prolactin can all matter.
Persistent Elevation or Suspected Pituitary Dysfunction
Where prolactin remains significantly raised without an obvious explanation, broader pituitary testing and clinical assessment may be appropriate.
The London Blood Tests Pituitary Function Profile measures prolactin alongside TSH, FSH, LH, growth hormone and cortisol.
Depending on the clinical findings and degree of elevation, further specialist investigation may include endocrinology assessment, pituitary imaging or visual-field testing.
Not every raised prolactin result requires an MRI. Investigation should be proportionate to the result and clinical picture.
How Can High Prolactin Affect Reproductive Hormones?
Persistent hyperprolactinaemia can suppress signalling within the hypothalamic-pituitary-gonadal axis.
In women, this can interfere with normal ovulation and menstrual cycling. Possible effects can include irregular periods, absent periods, difficulty conceiving and galactorrhoea, which means milk production or breast discharge outside normal breastfeeding.
In men, excessive prolactin can suppress reproductive hormone function and may contribute to reduced testosterone, lower libido, erectile dysfunction or fertility problems.
This does not mean that every menstrual, fertility or sexual symptom is caused by prolactin.
Thyroid disorders, polycystic ovary syndrome, menopause or perimenopause, medication, stress, obesity and many other health factors can produce overlapping symptoms.
The usefulness of the PRL blood test lies in answering one specific hormonal question within that larger picture.
Can Stress Affect a Prolactin Blood Test?
Yes.
Stress is particularly relevant to prolactin because even the stress associated with venepuncture itself can temporarily raise the hormone.
That does not mean every high result can be dismissed as stress.
Instead, stress becomes one factor to consider when a modest unexpected elevation is found, especially if the clinical picture does not otherwise suggest significant hyperprolactinaemia.
When repeat testing is recommended, avoiding strenuous activity beforehand and allowing yourself time to settle before sample collection may help reduce avoidable physiological influences.
Do You Need to Fast for a Prolactin Blood Test?
Preparation requirements vary between laboratories.
Some UK laboratory guidance recommends collecting prolactin at least one hour after waking and before eating. Other UK laboratories specify no special patient preparation at all.
There is therefore no single fasting rule that can be applied universally to every serum prolactin test.
The safest approach is to follow the preparation instructions supplied by the laboratory or healthcare provider performing your specific test.
London Blood Tests' general preparation guidance advises attending between approximately 7am and 12pm where possible and avoiding intense exercise for 24–48 hours before testing. Fasting is not automatically required for every test, but it may be recommended when other biomarkers are being collected at the same appointment.
If prolactin is being repeated because the first result was unexpectedly high, consistency in timing and preparation can make comparison more meaningful.
What Is the Normal Prolactin Range?
There is no single prolactin normal range that should be copied from one laboratory and applied to another.
Reference intervals depend on the laboratory method, analyser, sex and clinical circumstances.
Pregnancy and breastfeeding also substantially change expected prolactin concentrations.
For this reason, use the reference range printed alongside your own laboratory result rather than comparing your number with a random range found online.
The laboratory flag tells you whether the result falls outside that particular reference interval.
It does not, by itself, explain the cause.
Should Prolactin Be Tested With Other Hormones?
Sometimes.
It depends entirely on why testing is being performed.
For menstrual or fertility concerns, FSH, LH and oestradiol may provide useful additional context.
For male hormonal symptoms, testosterone, SHBG, LH and FSH may be relevant.
Where pituitary dysfunction is suspected, thyroid and adrenal-related hormones may also need to be assessed.
More biomarkers are not automatically better.
A targeted standalone prolactin test may be entirely appropriate when prolactin is the specific measurement required, whereas broader hormone profiles become useful when the clinical question involves several endocrine pathways.
What Does the London Blood Tests Prolactin Test Include?
The standalone London Blood Tests Prolactin Blood Test measures one biomarker: prolactin.
It is currently listed at £49, with a turnaround time of approximately 1–2 days.
Blood can be collected at a London clinic or through home phlebotomy where available, and samples are processed through UKAS-accredited laboratory services.
A standalone test can be useful when a healthcare professional has specifically requested prolactin or when an isolated measurement needs to be repeated.
When the reason for testing involves fertility, testosterone or broader pituitary function, a multi-hormone profile may provide more useful context.
Choosing the appropriate test is therefore less about ordering the largest panel and more about identifying the clinical question that needs answering.
When Should a High Prolactin Result Be Discussed With a Doctor?
An unexpected elevated result should be discussed with an appropriately qualified healthcare professional if it persists, is substantially above the laboratory range or occurs alongside relevant symptoms.
This is particularly important with persistent menstrual disruption, unexplained galactorrhoea, fertility problems, significant sexual dysfunction or symptoms that could indicate pituitary involvement.
Headaches or changes in vision also warrant medical assessment, especially if they are new or progressive.
A sudden severe headache, acute loss of vision or other sudden neurological symptoms requires urgent medical assessment rather than routine private blood testing.
Laboratory testing can identify abnormal hormone concentrations.
It cannot determine the full cause without clinical context.
Private Prolactin Blood Testing in London
London Blood Tests provides private prolactin blood testing in London for people who require either an individual prolactin measurement or a broader hormonal assessment.
The standalone Prolactin Blood Test is available with clinic and home blood collection and currently has a listed turnaround time of approximately 1–2 days.
Where additional hormonal context is needed, relevant options include the Pituitary Function Profile, Fertility Hormones Profile and Male Hormone Profile.
Private testing can make access to laboratory investigations more convenient, but an abnormal prolactin result should still be interpreted alongside symptoms, medication history, pregnancy status where relevant and the circumstances in which the sample was collected.
With prolactin, context matters.
Frequently Asked Questions About Prolactin Blood Tests
What does a prolactin blood test measure?
A prolactin blood test measures the concentration of prolactin, a hormone produced primarily by the pituitary gland. Prolactin is best known for its role in milk production but also interacts with reproductive hormone function.
What are high prolactin levels?
High prolactin levels mean the concentration is above the laboratory's reference range. Persistent elevation is called hyperprolactinaemia. The result does not identify the cause by itself.
What is a serum prolactin test?
A serum prolactin test measures prolactin in the serum portion of a blood sample. It is another commonly used term for prolactin blood testing.
What is a PRL blood test?
PRL is a common laboratory abbreviation for prolactin. A PRL blood test therefore refers to a prolactin measurement.
Can stress cause high prolactin?
Yes. Stress, including stress associated with venepuncture, may temporarily increase prolactin in some people.
Does high prolactin mean a prolactinoma?
No. Prolactinoma is one possible cause, but medicines, pregnancy, breastfeeding, hypothyroidism, kidney problems and physiological factors can also raise prolactin.
Do you have to fast for a prolactin test?
Not always. Preparation varies between laboratories. Some recommend testing before eating, while others specify no special preparation. Follow the instructions supplied for your test.
Can medication increase prolactin?
Yes. Some medicines, particularly certain dopamine-blocking antipsychotic medicines, can increase prolactin. Do not stop prescribed medication without advice from the clinician responsible for your treatment.
Can high prolactin lower testosterone?
Persistent hyperprolactinaemia can suppress reproductive hormone signalling and may contribute to reduced testosterone in men.
Can high prolactin affect fertility?
Yes. Persistent hyperprolactinaemia can interfere with ovulation in women and reproductive hormone function in men, although fertility problems can have many other causes.
What is macroprolactin?
Macroprolactin is a larger complex formed when prolactin binds to an immunoglobulin. It has less biological activity but can still be detected by some laboratory assays, causing an apparently raised total prolactin result.
Why might prolactin need to be repeated?
Because stress, exercise and sample circumstances can temporarily influence prolactin. A repeat test can help establish whether an unexpected elevation is persistent.
The Bottom Line
A prolactin blood test is straightforward to perform, but an elevated result can have several possible explanations.
One abnormal number does not automatically mean a pituitary tumour or serious endocrine disorder.
Stress, exercise, pregnancy, breastfeeding, medication, thyroid function, kidney function and macroprolactin may all need to be considered. When high prolactin levels remain present, the wider hormone picture and clinical symptoms help determine what should happen next.
The useful question is therefore not simply:
"Is my prolactin high?"
It is:
"Why is it high, and is the elevation persistent?"
For private testing, London Blood Tests offers a standalone Prolactin Blood Test as well as broader pituitary, fertility hormone and male hormone profiles where additional biomarkers are clinically relevant.
Results should always be interpreted in the context of symptoms, medication and wider health information rather than in isolation.
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