Endocrine Abstracts

Background: Recent studies have indicated that macroprolactinaemia accounts for up to 26% of biochemical hyperprolactinaemia depending on the assay in use. Delayed metabolic clearance of macroprolactin together with detection by most automated prolactin immunoassay systems leads to pseudo-hyperprolactinemia in patients harbouring this form of complexed prolactin.

We here describe the use of serial macroprolactin measurement to assist in the management of a pregnant lady with pre-conception hyperprolactinaemia.

Case report: A 24-year-old lady was found to have a raised prolactin level of 2332 μ/l (0–500). Thyroid function was normal. Prolactin was checked because of primary infertility in the context of a normal menstrual cycle. Before MRI imaging of the pituitary gland could be performed she fell pregnant. Macroprolactin screening (using PEG precipitation) was positive, accounting for 54% of measured prolactin (estimated monomeric prolactin 1072 μ/l). As expected, measured prolactin rose through pregnancy to 6975 μ/l at 20 weeks and to 8374 μ/l at 36 weeks gestation. However adjustment for macroprolactin gave estimated monomeric prolactin levels of 2370 at 16 weeks (macroprolactin 66%) and 2596 μ/l at 36 weeks (macroprolactin 69%). Thus adjusted prolactin fell within the normal range for pregnancy. She remained well throughout pregnancy. Visual fields were formally assessed serially though pregnancy with no abnormality identified. Pregnancy went to term with a healthy boy delivered. MRI scan pituitary performed post-partum showed a right sided pituitary adenoma, maximum diameter 5mm with evidence of central necrosis/haemorrhage. She is currently breast feeding.

Discussion: Serial measurement of macroprolactin with estimation of monomeric prolactin greatly enhanced clinical management through pregnancy and saved unnecessary further investigations.

As previously reported, the proportion of macroprolactin increased through pregnancy.

We advocate the reporting of ‘adjusted’ monomeric prolactin to inform patient assessment in cases of hyperprolactinaemia rather than simply stating ‘macroprolactin positive’.