The epidemiology of hyperprolactinaemia is not well characterised in the literature. Using unique patient identifier we were able to link data from biochemistry, prescribing, hospital admissions, radiology, general registry office and maternity data. Observational data was collected for Tayside Scotland between 1993 and 2013. Any patient with a serum prolactin measurement >1000 mU/l or at least three prescriptions for a dopamine agonist were included. Patients who were pregnant at the time of assay were excluded, unless they had raised prolactin at other times out-with pregnancy. Patients were then categorised into four groups. Patients with a serum prolactin >5000 mU/l or use of dopamine agonists were classed as having a probable pituitary tumour (group 1). Patients who had a record of being prescribed antipsychotics, tricyclics, SSRIs, dopamine antagonists, opioids, H2 antagonists, verapamil, and methyldopa 6 months before or one after the raised prolactin who did not fit into group 1 were classed as drug induced hyper-prolactinaemia (group 2). Patients who had macroprolactin identified without any other explanation, or who had high concentrations of macroprolactin were classed as having macroprolactin (group 3). The remainder were unclassified (group 4).
Overall 32 289 patients had a serum prolactin assay undertaken, of which 1366 were >1000 mU/l, of which 65 were during pregnancy. 334 patients were identified as having a pituitary tumour, 415 were drug related, and 174 were due to macroprolactin, thus leaving 378 idiopathic cases. The average prevalence of hyper-prolactinaemia was 107/100 000 of the population, and the incidence rate over the last 20 years was 14 cases/100 000 person-years. Drug induced hyper-prolactinaemia was the commonest cause of raised serum prolactin.