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Prolactin

Chemical Pathology

Notes

  • Prolactin is a peptide hormone secreted by the anterior pituitary, which has many actions but is essential in particular for normal production of human breast milk.
  • Control of prolactin is through the suppressive effect of dopamine from the hypothalamus.
  • Prolactin levels are measured when patients have a suspected pituitary tumour (prolactinoma), and in the investigation of oligomenorrhoea, amenorrhoea, galactorrhoea or infertility in women and hypogonadism, impotence and infertility in men.
  • Raised prolactin levels may result from normal pregnancy and lactation, many drugs, particularly the anti-psychotic agents that act via dopamine metabolism or dopamine receptors, renal failure, stress, including that associated with venepuncture, exercise, seizures, hypothyroidism (prolactin is stimulated by the raised TRH) and other pituitary disease.
  • When a significantly raised prolactin level is found, the presence of macroprolactin needs to be excluded. Macroprolactin is a biologically inert polymeric form of prolactin in which prolactin molecules combine with circulating immunoglobulin. Samples with prolactin >700 U/L are therefore checked for the presence of macroprolactin.
  • For follow up samples, if found to be negative for macroprolactin within the last 12 months then the macroprolactin check would not normally be repeated within this time period.

Sample requirements

  • Ideally samples should be collected at least 1 hour after waking and before eating.
  • Physiological causes of increased prolactin (e.g. stress, strenuous exercise, pregnancy, breast palpation, nipple stimulation) should be avoided prior to collection of specimen.
  • If patient on high dose biotin therapy (>5mg/day) collect sample at least 8 hours after the last dose.

For adults, blood taken into a 5mL gold top gel tube (or rust top for the Acute Unit)

Gold top with cap

For children, blood taken into a 3.5mL rust top gel tube

3.5ml rust top tube

For neonates, blood taken into a 0.8mL minicollect lithium heparin tube.

Minicollect lithium heparin tube

Storage/transport

Send at ambient temperature to the laboratory. If unavoidable samples can be stored refrigerated overnight.

Required information

Relevant clinical details including full drug history (especially if on any anti-psychotic medication).

Turnaround times

Samples are processed throughout the day at GRH with results normally available within less than 24 hours, however if samples require checking for the presence of macroprolactin (initial prolactin >700 mIU/L) and not recently checked, then the turnaround time will be 7-10 days.

Reference ranges

Reference range: <700 mIU/L.

Please note: 95% of female patients will have a prolactin result of <500 mIU/L and 95% of male patients will have a prolactin results of <325 mIU/L. Results of 500 - 700 mIU/L for female patients and 325 - 700 mIU/L for male patients are rarely pathological and are likely due to stress of venepuncture.

  • The prolactin assay has been calibrated against the 3rd IRP WHO Reference Standard 84/500.

Further information

To learn more about prolactin, visit Lab Tests Online

For more detailed information on the investigation and management of prolactinoma, visit Endobible

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