This study investigated the differences in clinical and laboratory features as well as treatment response in 70 outpatients with macroprolactinemia and monomeric
hyperprolactinemia treated with
dopamine agonists. After precipitation of the patients' serum samples with poly-
ethylene-glycol (PEG), serum
prolactin (PRL) levels were measured. We also measured serum levels of
luteinizing hormone (LH),
follicle-stimulating hormone (FSH),
estradiol for women and
testosterone for men. Clinical symptoms and signs were recorded. All patients received brain magnetic resonance imaging (MRI). After excluding patients with macroadenoma, 66 patients were treated with the
dopamine agonist cabergoline. After 1 year, the clinical responses to
cabergoline were recorded and PRL levels measured. Of the initial 70 patients with
hyperprolactinemia, 15 patients (21.4%) were found to have macroprolactinemia, while the rest had monomeric
hyperprolactinemia. The two groups did not differ with regard to
galactorrhea, menstrual disturbances or
impotence. There were no significant group differences in serum LH, FSH,
estradiol or
testosterone levels. Patients with macroprolactinemia, however, had a significantly lower
infertility rate than those with true
hyperprolactinemia (6.7% vs. 32.7%, p=0.005). A greater percentage of macroprolactinemic patients had normal MRI pituitary images than those with
hyperprolactinemia (73.3% vs. 34.5%, p=0.029). Compared to those with true
hyperprolactinemia, patients with macroprolactinemia were found to have no significant changes in clinical features and PRL levels after 1 year of
cabergoline therapy (after PEG precipitation, pre- and post-PRL levels: 59.3 ± 100.2 to 13.8 ± 9.5 ng/mL vs. 6.1 ± 5.3 to 5.1 ± 4.3 ng/mL, p=0.002). In conclusion, while macroprolactinemia is a common cause of
hyperprolactinemia, many clinical and laboratory features cannot be used reliably to differentiate macroprolactinemia from true
hyperprolactinemia. Routine screening for all hyperprolactinemic sera with PEG might prevent the unnecessary use of image studies and medical treatments for people with
hyperprolactinemia.