PRL and pituitary gland adenoma: In a British study (n = 226), prolactin levels > 2,000 mU/L (94 ng/mL) were observed only in 3 cases of nonfunctioning pituitary adenomas (1.3%) and the maximum values were 3,257 mU/L (153 ng/mL) and 2,565 mU/L (120 ng/mL) in patients taking and not taking drugs capable of increasing prolactin levels, respectively (21).