Endocrine Abstracts

Objective: Macroprolactinaemia is the phenomenon of forming immunoglobulins (Igs) against prolactin (PRL). The Ig–PRL complex has an increased half-life resulting in elevated levels of immunoreactivity in most PRL immunoassays without having any significance. Identifying macroprolactinaemia-induced hyperprolactinaemia is essential in order to prevent unnecessary testing and treatment. This study is to establish the combined intra- and inter-individual variability in macroprolactinaemia and to verify if multiple measurements to diagnose macroprolactinaemia are justified.

Method: Macroprolactinaemia was determined by size-exclusion chromatography (SEC) combined with the AutoDelfia PRL immunoassay. The percentages of monomeric PRL (%PRL), dimeric PRL (%BIG–PRL) and Ig–PRL complex (%BIG–BIG–PRL) were calculated. Abnormal macroprolactinaemia was diagnosed if the measured %PRL > reference %PRL. From a group of 298 patients suspected for macroprolactinaemia and subjected to SEC combined with immunological testing, 17 patients, who had undergone multiple testing, were selected; 15 patients had been tested twice and two patients three times. The combined intra- and inter-individual variability was calculated based on inter-individual coefficient of variance (CV) of the relative intra-individual change (RIC) according to the model of running means between two time points: RIC=(abs(A−B))/((A+B)/2)×100% in which A is the percentage of the respective PRL form at one time point and B that of the subsequent time point.

Results: CVs of %PRL, %BIG–PRL and %BIG–BIG–PRL were 21, 32 and 27% respectively. The period between the time points was not standardized, varied significantly and was 16±19 months (mean±S.D.; n=19). The presence of absence of abnormal macroprolactinaemia proved to be unchanged in subsequent samples; 12 patients suffered from abnormal macroprolactinaemia of which nine patients had normoprolactinaemia after correction.

Conclusion: The combined intra- and inter-individual variability’s of the PRL forms were ≤33% and the diagnosis of macroprolactinaemia was consistent during the time period evaluated. Therefore, no indications were found that justify multiple measurements to diagnose macroprolactinaemia.

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.