Clinically, a diagnosis of hyperprolactinaemia can only be made when serum PRL levels are elevated on two separate occasions [166] and a careful diagnostic work-up is required, given that the cause may be broadly categorised as physiological (including stress and exercise), pharmacological (dopamine receptor antagonists, oral contraceptive pill), or pathological (prolactinoma, liver cirrhosis, polycystic ovarian syndrome, chest wall trauma, and seizures). This evidence concerns the gene PRL and Increased circulating prolactin concentration.