Endocrine Abstracts

Macroprolactinaemia, a common phenomenon variably expressed in different assays, influences interpretation of prolactin results, as recognised since 1978. The degree of macroprolactinaemia manifest over time is less well described. We examined how macroprolactin status (based on polyethylene glycol(PEG) precipitation prolactin % recovery) varied over serial measurements in hyperprolactinaemic individuals.

Methods: All serum total prolactin results(measured using Roche-Cobas-8000-analysers) were extracted from the laboratory-information system for the period 1January 2011 to 1April 2021, along with relevant patient demographic/test data. Of these, samples with a macroprolactin(% recovery) screening test performed (on samples with prolactin >700 iu/l) were included in the main analysis.

Results: 2782 macroprolactin checks were performed during the study period(12.5% of all prolactin tests) in 1810 individuals (median age=35 (IQR:25-47, range=16-93) years; male=599, female=2183). Of these, 465 patients had more than one macroprolactin test(totalling 1437 samples tested). 141 tests were macroprolactin screen positive(<60% recovery) in 94 patients. Only 19 patients (18 female) had at least one result above + one below the 60% screening cut-off. Of these, 10 patients had results around cut-off borderline, 3 had clearly different results, 6 appeared to be errors based on other previous/later/confirmatory results. In terms of clinical details, 6 were on antidepressants/antipsychotics, 4 had prolactinoma, 1 was pregnant, 2 on OCP, 1 on levothyroxine.

Conclusion: In this study, very few patients appeared to change macroprolactin status (between positive/negative) based on the PEG%recovery cut-off. Of the 19 that did, the majority were on antipsychotic/antidepressant medication or had a prolactinoma; only three appeared to have clear deviation in the %recovery. This suggests that once macroprolactin status is determined, it is unhelpful to repeat, except where there is clinical discordance between result vs patient’s condition, or a new prolactinoma diagnosis/significant change to medication/prolactin level.