140 Cases of Macroprolactinemia: Selected Clinical and Technical Laboratory Aspects

Background: Macroprolactinemia can be an overlooked cause of hyperprolactinemia. To document the presence of macroprolactin in serum indirectly, an initial precipitation of the complexed prolactin (PRL) using polyethylene glycol (PEG) is followed by measurement of free and total prolactin by immunoassay. Objectives: Adaptation of the PEG method to our PRL immunoassay to detect cases with predominant macroprolactinemia and to study the short- and long-term changes of the relationship between PRL forms. Patients and Methods: One hundred forty hyperprolactinemic patients (aged 17-72 years) in whom macroprolactin constituted . 60% of the total PRL were included in our study. The predominance of macroprolactin was measured by adapted PEG procedure, followed by immunoradiometric and chemiluminescence methods. Long-term observations with repeated serum PRL measurements were made in 20 cases. For another 20 of 41 patients with indications for metoclopramide (MCP) stimulation test, we analyzed short-term alterations in free and complexed PRL levels. Results: Adjustment of the PEG method by testing samples in dilution minimized the interference of PEG in the immunoassays and let proper detection of predominant macro- prolactinemia. During the long-term observations, the ratio of macroprolactin to total PRL remained relatively constant, independent of changes in total PRL levels. During the MCP test, in the majority of patients with macroprolactinemia (except those with associated PRL-secreting adenoma), an acute rise of PRL level followed by a rise in macroprolac- tin resulted in a short-term decrease in macroprolactin/total PRL ratio. Conclusions: Confirmation of the predominance in serum of macroprolactin explains the discordance between the raised PRL level and scant of absent symptoms characteristic for hyperprolactinemia. Its proper detection can influence further management.