PRL and non-functioning pituitary adenoma: In a retrospective analysis of 117 patients with prolactinomas and NFPAs, it was found that NFPA patients most often had a prolactin (PRL) level < 100 ng/mL (~ 2000 IU/L) whereas levels > 250 ng/mL (~ 5000 IU/L) were exclusively seen in patients with prolactinomas [37].