Physiological, pharmacological, pathological and the stalk effect
Expansion
Physiological: pregnancy, breastfeeding, nipple stimulation, stress, sleep, venepuncture itself.
Pharmacological (the commonest cause in practice): dopamine antagonists including antipsychotics (especially risperidone and amisulpride), metoclopramide and domperidone, plus oestrogens, opiates, methyldopa and verapamil.
Pathological
- Prolactinoma: microadenoma or macroadenoma
- Stalk effect: any lesion compressing the pituitary stalk interrupts the tonic dopamine inhibition, so prolactin rises modestly (usually under 2000 mU/l) while other pituitary hormones fall
- Hypothyroidism: raised TRH stimulates prolactin
- Chronic kidney disease, cirrhosis, chest wall injury, polycystic ovary syndrome
Presentation: galactorrhoea, amenorrhoea or oligomenorrhoea and infertility in women; loss of libido, erectile dysfunction and gynaecomastia in men, who therefore present later and with larger tumours.
Two pitfalls: macroprolactin, an inactive complex causing a spuriously high result, and the hook effect, where extremely high levels saturate the assay and give a falsely low reading, which is avoided by diluting the sample.