One form of prolactin (PRL) is macroprolactin with high molecular mass. Many macroprolactinemic patients have no pituitary adenomas and no clinical symptoms of hyperprolactinemia, it is controversial whether macroprolactinemia is a benign condition that does not need further investigation and treatment. In this study, we aimed to compare macroprolactinemic patients (group I) with the true hyperprolactinemic patients (group II) for the presence of pituitary adenoma. We investigated 161 patients with hyperprolactinemia, whose magnetic resonance imaging records of the pituitary were taken. All patients were questioned for irregular menses, infertility and examined for galactorrhea. Patients were screened for macroprolactinemia by polyethylene glycol precipitation, and a recovery of ≤40% and normal monomeric PRL level was taken as an indication of significant macroprolactinemia. Of 161 patients with hyperprolactinemia, 60 (37.26%) had macroprolactinemia. PRL levels of group II were lower than those of group I (P = 0.011), although monomeric PRL levels of group II were higher than those of group I (P = 0.0005). Of 60 macroprolactinemic patients, 16 (26.7%) had pituitary adenomas. The prevalence of pituitary adenomas was lower in group I, compared with group II (P = 0.0005). No significant differences were found between the prevalences of irregular menses and infertility of group I and II (P = 0.084, P = 0.361). Prevalence of galactorrhea in group I was lower than that in group II (P = 0.048). Prevalence of pituitary adenomas in macroprolactinemic patients is lower compared with the true hyperprolactinemic patients, but may be higher than that found in other recent studies and in the general population.
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