Endocrine Abstracts

Design: Macroprolactinemia may influence the interpretation of serum prolactin levels – a recognised phenomenon since 1978¹. The degree of macroprolactinaemia over time is less well described. We determined how macroprolactin status (based on polyethylene glycol (PEG) precipitation varied by analysing serial measurements in hyperprolactinaemic individuals over nine years.

Patients and Measurements: Results from 1810 individuals were included. All serum total prolactin results (measured using Roche Cobas 8000 analyser) were extracted from the laboratory information system from 1 January 2012 to 1 April 2021, along with relevant patient demographic/test data. Samples with a macroprolactin screening test performed (on samples with prolactin >700 mu/l) were included in the main analysis.

Results: During the study period, 2782 macroprolactin checks were performed (12.5% of all prolactin tests) in 1810 (599 males/2183 females, median-age: 35, IQR:25-47, range:16-93 years) individuals. Multiple macroprolactin checks were carried out on 465 patients (1437 measurements) (see Table 1) with 94 patients (141 measurements) screening positive (<60% recovery). Only 19 patients (18 female) had at least one result above and one below the 60% screening cut-off. In terms of clinical details, six were on antidepressants/antipsychotics, four had a prolactinoma, one was pregnant, two were on an oral contraceptive pill (OCP) one person was on levothyroxine, and in five further clinical details were unavailable. 10 of these patients had results close to the 60% cut-off. 5 had clearly different results; 4 appeared to be outliers based on other results. In 7 cases the adjusted monomeric prolactin showed a potentially clinically significant difference.

Conclusions: In this study, only 19/465 patients appeared to change macroprolactin status based on a 60% PEG recovery cut-off. The majority of these 19 patients were on antipsychotic/antidepressant medication(s) or had a prolactinoma; In only 7 monomeric prolactin changed significantly. This suggests that once macroprolactin status has been determined, clinical decision-making is rarely affected by repeating it.

Reference: 1. Heald, A., Blantern, E., Anderson, S., Radford, D., et al., Quantitative adjustment for macroprolactin is an integral part of laboratory assessment of hyperprolactinaemia. Experimental and Clinical Endocrinology & Diabetes 2012, 376–380.