Endocrine Abstracts

Background: The so called ‘big-big’ prolactin, also known as macroprolactin is formed by prolactin-immunoglobulin complexes, is considered to be biologically inactive, but may cause elevation of serum prolactin (Prl) concentrations measured by standard assays. In women presenting with oligo- and/or amenorrhoea the cause of menstrual irregularity needs to be explained even in the setting of concomitant macroprolactinaemia. We have therefore attempted to assess the prevalence of pituitary pathology in women with macroprolactinaemia and oligo-/amenorrhoea.

Material and methods: We performed pituitary MRI scans in 60 women with oligo- and/or secondary amenorrhoea aged 31.0±6.7 years (mean±S.D.), range 18–45 years who were found to have raised Prl concentrations due to macroprolactinaemia, detected by the polyethylene glycol (PEG) precipitation method.

Results: After PEG precipitation of macroprolactin, ‘free’ Prl concentrations were still raised (i.e. above 530 mIU/l) in 35 (58%) women with macroprolactinaemia. Furthermore, pituitary microadenomas were detected in 9/60 (15%) and pituitary macroadenomas in 3/60 (5%) of women with macroprolactinaemia and oligo-/amenorrhoea. In all of these cases there was a concomitant elevation of ‘free’ Prl after PEG precipitation. The highest value of ‘free’ Prl was in a case of microadenoma (total Prl 19207 mIU/l, ‘free’ Prl after PEG precipitation 7738 mIU/l), while in the case of macroadenoma the highest concentration of ‘free’ Prl was 2798 mIU/l (total Prl 7441 mIU/l before PEG precipitation). Hence, in case of coexistence of macroprolactinaemia and raised ‘free’ Prl after PEG precipitation of macroprolactin, the chance of finding of either a micro- or a macroadenoma was as high as 34% (12 cases out of 35).

Conclusions: Hyperprolactinaemia and macroprolactinaemia may coexist in the same patient. If ‘free’ prolactin is still raised after PEG precipitation of macroprolactin, then the chance of finding of a pituitary micro- or macroadenoma in women with oligo-/amenorrhoea is about 30%. Therefore pituitary magnetic resonance imaging is mandatory in all such cases.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.