This will require a systematic evaluation by a specialist trained in Reproductive Endocrinology to determine which of the above mentioned conditions is responsible for anovulation. Diagnosis is not always straightforward (e.g. for diagnosing hypothalamic amenorrhoea) and requires highly specialised expertise in Reproductive Endocrinology in combination with blood tests for measuring the levels of a range of hormones.
For details on making the diagnosis of PCOS, see my section on PCOS.
Investigating for hyperprolactinaemia involves measuring the levels of active prolactin in the blood. This will need to take into account the levels of inactive circulating prolactin (or macroprolactin). Other relevant investigations could include MRI scanning of the brain if a pituitary tumour is suspected.