PRL and hyperprolactinemia: On the other hand, while PRL levels > 100 ng/ml should raise suspicion for prolactinoma, moderately high PRL levels (25–100 ng/ml) in absence of recognizable causes of hyperprolactinemia, defined as HomeoFIT-PRL, may represent a physiological response to transient stimuli requiring an increase in metabolic demand (e.g. insulin-induced hypoglycemia, stress, sexual arousal, intense exercise, circadian peaks), aimed to promote metabolic adaptation [62, 63].