Investigations of hyperprolactinaemia

Useful investigations include:

• MRI/CT scan of the brain
• formal assessment of the visual fields:
  • this will detect damage to the optic nerve chiasm secondary to a pituitary tumour

Other investigations include:

• loss of normal diurnal fluctuation in prolactin levels
• loss or reduction in response to TRH injection - normal increases x 500
• loss of response to metoclopramide - normal increases x 2000

What level of prolactin is significant?(1)

• mildly increased prolactin levels (400-600mu/L) may be physiological and asymptomatic but higher levels are usually pathological
  • should be repeated to confirm hyperprolactinaemia
• very elevated levels (above 5,000mu/L) usually imply a prolactin-secreting pituitary tumour

Note that reference ranges vary between laboratories.

Notes:

• prolactin secretion varies with time, resulting in serum levels being 2-3 times higher at night than during the day. The levels of prolactin in normal individuals also tend to rise in response to physiological stimuli, including sleep, exercise, pregnancy and surgical stress (2)
• most patients with a prolactinoma are women

Reference:

• GPonline. Hyperprolactinaemia: diagnosis and management (Accessed July 28th 2018)
• South Tees Hospitals NHS Foundation Trust. Prolactin. (Accessed July 28th 2018)