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Reference Range

Min : 102
Max : 496

Min : 86
Max : 324

Test Usage

Prolactin is secreted by the anterior pituitary gland and induces lactation. Normally, prolactin is secreted in a pulsatile, sleep dependent rhythm with highest levels occurring during sleep and lowest levels occurring a few hours after waking. Prolactin secretion by the pituitary gland is under tonic inhibition from the hypothalamus via dopamine. Any lesion of the pituitary stalk prevents tonic inhibition and allows prolactin levels to rise. Prolactin concentrations normally rise with illness and physical stress. If pharmacologic doses of thyrotrophin releasing hormone (TRH) are administered, prolactin concentrations can increase.

Suggested guidance for elevated prolactin of unknown cause:

For prolactin results 700 – 2000 mIU/L: 

Moderately elevated prolactin. Consider causes including renal insufficiency; hypothyroidism; medications such as OCP and some antipsychotics, antidepressants or antiemetics; PCOS; recent or ongoing stressful events; excessive exercise; breastfeeding. Where applicable rule out pregnancy. On a first-time raised prolactin of 700 mU/L or greater, the laboratory will rule out a known spurious cause of hyperprolactinaemia called “macroprolactin”.

If no clear cause is identified, a repeat measurement of prolactin is suggested. The sample should be taken at least 1 hour after waking, where applicable at day 1 to 4 of the follicular phase and if possible after any stressful circumstance/event has resolved. Advise the patient to sit quietly for 15 minutes in the waiting room prior to the blood test. If prolactin remains elevated at a similar or higher level consider discussing with endocrinology.


For prolactin results >2000 mIU/L: 

Marked elevation of prolactin. Rule out pregnancy, breastfeeding or any drugs known to cause substantial elevation of prolactin e.g. some antipsychotics or antidepressants. On a first-time raised prolactin of 700 mU/L or greater, the laboratory will rule out a known spurious cause of hyperprolactinaemia called “macroprolactin”.
If the above are ruled out, discussion with endocrinology is appropriate.


Macroprolactin is a high molecular weight complex composed of prolactin attached to antibodies or other constituents. This complex can be found in some people’s serum. Macroprolactin has no clinical significance but it can sometimes cause positive interference in prolactin assays i.e. results are falsely high. We automatically perform a check for macroprolactin on all samples with a prolactin of 700 mIU/L or above where a check has not already been performed in the last 5 years. The macroprolactin check uses PolyEthylene Glycol (PEG) precipitation to remove the macroprolactin from serum. The remaining (true) prolactin in serum is then measured and compared to the amount originally measured. This gives a percentage recovery. A recovery of less than 60% suggest that macroprolactin may be present. If this is the case we will report a “monomeric” prolactin which gives an indication of the amount of actual prolactin hormone present with a reference range to aid interpretation. If the macroprolactin recovery is above 60% we do not report any results for macroprolactin testing as feedback from our service users indicated that this was unnecessary and potentially confusing.

Turnaround time

1 day


Local test

Can be added on to an existing request up to 4 days following sample receipt

Specimen Labelling Procedure
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