While several studies assess the cut-off PRL value that could differentiate between a prolactinoma and a non-functioning pituitary adenoma9,14,15, and cut-off differentiating between a prolactinoma and “stalk effect” hyperprolactinemia, to the best of our knowledge, this is the first study reporting on a value that distinguishes micro- from macro- prolactinomas. Here, PRL is linked to hyperprolactinemia.