Macroprolactin is a high molecular weight IgG-prolactin complex which has reduced bioactivity. Macroprolactinaemia is a relatively common phenomenon, accounting for upto 20% of cases of hyperprolactinaemia in clinical practice; in the absence of amenorrhoea or hypogonadism these patients do not usually need dopamine agonist therapy. To ensure appropriate detection and management of such patients we routinely screen all serum samples with hyperprolactinaemia (>600 mU/l) for macroprolactin, and report positive samples with a quantitative estimate of macroprolactin content. We have performed a retrospective case-note study of 25 macroprolactin patients to assess the clinical interpretation of mPRL reporting. The presence of macroprolactin was recorded and interpreted appropriately in 19 cases (76%); in the remaining 6 cases the finding of macroprolactin as the major prolactin form, though reported by the laboratory, was not noted by the clinician (gynaecology 5, neurology 1); furthermore there was no evidence that the macroprolactin result had been taken into account in subsequent management. Pituitary imaging was performed in 13 cases; 10 were normal and 2 showed a small focal lesion suggestive of a microadenoma. In one case imaging showed a pituitary mass; in this man macroprolactin was a minor component of his hyperprolactinaemia (PRL 3865 mU/l, 20% macroprolactin), and he was treated with bromocriptine for a prolactinoma. One patient with hyperprolactinaemia due to macroprolactin (PRL 738 mU/l, 24% macroprolactin) had normal menses but galactorrhoea which resolved with bromocriptine. This study demonstrates that there is still misunderstanding by clinicians of the relatively common finding of hyperprolactinaemia caused by macroprolactin. Patients with macroprolactinaemia and galactorrhoea may benefit from bromocriptine. The case of prolactinoma causing significant hyperprolactinaemia with only a minor macroprolactin component highlights the importance of quantitative reporting of macroprolactin: in contrast to the majority of macroprolactinaemia patients, such cases do warrant imaging and treatment with dopamine agonist therapy.
22 - 24 Mar 2004
British Endocrine Societies