Objective： To establish a polyethylene glycol (PEG6000) precipitation method for screening macroprolactinemia in patients with high serum prolactin (PRL). Methods： PEG6000 precipitation method was used to remove macroprolactin (MPRL) molecules in serum of PRL-elevated patients. The effect of PEG6000 precipitating serum MPRL was determined by Sephacryl S-100HR chromatography plus chemiluminescent immunoassay and SDS-PAGE plus Western Blot assay. The PEG6000 precipitation plus chemiluminescent immunoassay was applied to screen serum samples of PRL-elevated patients for macroprolactinemia. The clinical manifestations of patients with true-hyperprolactinemia, hyperprolactinemia/macroprolactinemia or true-macroprolactinemia were analyzed and compared.Results： After precipitation with PEG6000, MPRL peak or hybridization signal in the serum samples was markedly decreased, while the big or small prolactin (BPRL or SPRL) levels were not affected. In 1538 PRL-elevated patients, 16.1% (247/1538) were detectable for macroprolactinemia, while the 83.9% (1291/1538) were identified as true-hyperprolactinemia. In 247 samples of macroprolactinemia, 93.5% (231/247) were determined as true-macroprolactinemia, while 6.5% (16/247) were identified as hyperprolactinemia plus macroprolactinemia. In 508 true-hyperprolactinemia patients, menoxenia, menolipsis/menostasia, dysgenesia or hypophysoma were manifested in 438 (86.2%), which were also manifested in 85.7% (6/7) of hyperprolactinemia/macroprolactinemia patients. However, only 11 cases in 71 true-macroprolactinemia patients (15.5%) presented above clinical diseases.Conclusion： There is a certain proportion of true-macroprolactinemia (pseudo-hyperprolactinemia) in serum PRL-elevated patients. The PEG6000 precipitation method established in this study can efficiently distinguish true-hyperprolactinemia from pseudo-hyperprolactinemia in patients.