<prompt> Investigation of choice of hyper-prolactinemia-TRH estimationLH estimationProlactin estimationEstradiol estimation  <response>: Basal, fasting morning prolactinPRL levels normally 20 mgL should be measured to assess hypersecretion in hyperprolactinemia. In non-pregnant and non-lactating patients, monomeric prolactin concentrations of 500-1000 mUL are likely to be induced by stress or drugs, and a repeat measurement is indicated. Levels between 1000 and 5000 mUL are likely to be due to either drugs, a microprolactinoma or disconnection hyperprolactinaemia. Levels above 5000 mUL are highly suggestive of a macroprolactinoma. Reference : page 791 Davidsons Principles and practice of Medicine 22nd edition 