ABSTRACT
Background: Macroprolactin is biologically inactive but may be detected by immnoassays. This leads to errors in diagnosis and inadequate treatment of patients with hyperprolactinemia. Aim:To assess two techniques to detect the presence of macroprolactin. Material and Methods: Prolactin was measured by immunoassay in 57 serum samples (from 4 males and 53 females aged33 +/- 13 years), before and after precipitation with polyethyleneglycol (PEG) and separation by ultrafiltration. A significant level of macroprolactin was considered to be present when prolactin detected in the supernatant after PEG precipitation or in the ultrafiltrate was less than 40 percent of the initial concentration of prolactin. Results: Prolactin levels fluctuated from 5 to 411 ng/ml. The percentages of recuperation were independent of the initial prolactin concentration. In 12 and 14 percent of samples, using polyethyleneglycol and ultrafiltration respectively, there was a prolactin recuperation of less than 40 percent. Eight and 11 percent of samples with a prolactin concentration of more than 30 ng/ml, had a recuperation of less than 40 percent using polyethyleneglycol and ultrafiltration respectively. Conclusions: Approximately 10 percent of samples with a prolactin concentration over 30ng/ml have recuperation values suggestive of the presence of macroprolactin. There is a good concordance between precipitation using polyethyleneglycol or ultrafiltration.