HP was detected in 76 (46.1%) of the 165 patients in the serial measurement group and 72 (69.9%) of the 103 patients in the single measurement group (p<0.001). Of the 148 detected patients with HP, 1 had prolactinoma as a component of multiple endocrine neoplasia 1 (MEN1), and 1 had cosecretion of PRL with acromegaly. This evidence concerns the gene PRL and multiple endocrine neoplasia type 1.