Prolactin (Blood)

Diagnostic Use

Prolactin measurements may be helpful in the investigation of galactorrhoea, amenorrhoea, infertility or hypogonadism. Mildly raised levels (up to 2 to 3 times the upper reference limit) are common and can be due to many causes.

Causes of a raised prolactin

• Prolactinoma
• Drugs: All classes of psychotropic drugs, including dopamine-antagonists ( phenothiazine-type antipsychotics, antihistamines, and antiemetics e.g. metoclopramide),  atypical antipsychotics, anti-depressants (tricyclics, SSRIs, MAOIs), cannabinoids, amphetamines, buspirone, alprazolam, domperidone, alpha-methyldopa, reserpine, verapamil, morphine, H2 antagonists, fenfluramine, physostigmine, estrogens (including OC).
• Physical or psychological stress (illness, anaesthesia, surgery).
• Non-functioning pituitary tumours causing pituitary stalk compression.
• Macroprolactin : an elevated prolactin concentration may be due to the presence of macroprolactin, a biologically inactive prolactin-immunoglobulin complex which is cleared slowly from the plasma. The presence of macroprolactin has no clinical consequences, but may lead to unnecessary investigations.

At LabPlus, all samples with a raised prolactin concentration are routinely tested for the presence of macroprolactin.  The level of monomeric (biologically active) prolactin is reported, as well as the total prolactin (monomeric prolactin + macroprolactin).  If the monomeric prolactin is normal, no further investigations for prolactinoma are necessary.

• Post-seizure :  Prolactin may be elevated following a convulsion. Blood needs to be taken within 40 min of the event, and should be compared with a baseline sample taken before the event or a sample taken several hours later.  However, a normal prolactin level does not discriminate between partial seizures (complex or simple) and non-epileptic events.  The prolactin release may be blunted in the case of repetitive seizures.
• Diurnal variation: prolactin levels are highest in early morning
• Pregnancy: can peak up to 10,000 mIU/L in late pregnancy.
• Lactation: peaks at 10 min. after starting breast feeding
• Sexual intercourse.
• Hypothyroidism
• PCO syndrome

References

1. Daria La Torre et al.   Pharmacological causes of hyperprolactinaemia.  Therapeutic and Clinical risk management 2007; 3(5): 929-951

2. Kyle, C. Sonic Pathology Handbook, 2014.

Reference Intervals

Units: mIU/L

Reference ranges

Conversion factors

mIU/L = ng/mL x 21.2

mIU/L = ug/L x 21.2

ng/mL x 21.2 = mIU/L