A prolactin level above 100ug/L indicates a high probability of pituitary prolactinoma. Prolactin levels in the blood are closely related to the size of the prolactinoma; the larger the prolactinoma, the higher the prolactin level in the blood. Prolactin levels greater than 200ug/L are often indicative of a pituitary macroadenoma; mildly elevated prolactin may be a result of stress or test error, so blood prolactin levels can be repeated. In the case of hyperprolactinemia caused by drugs that stimulate prolactin secretion, such as metoclopramide, chlorpromazine, and cimetidine, the elevated prolactin level will not meet the diagnostic criteria for pituitary prolactinoma. Therefore, prolactin levels can help determine if it is a pituitary prolactinoma, preferably in combination with imaging, of course.