Clinical Impact of New Reference Intervals for the Roche Prolactin II Immunoassay

Abstract

Dear Editor, Recently, a new upper limit of normal (ULN) range for the Roche Prolactin II immunoassay has been proposed by Earll et al. [1] The authors investigated 374 serum samples from healthy outpatients and suggested a new ULN for the Roche II assay of 37.8 ng/mL or 804 mIU/L (females) and 22.8 ng/mL or 485 mIU/L (males). They concluded that adopting these reference intervals would not delay diagnosis or prevent necessary intervention in patients with clinically significant pituitary tumours but reduces unnecessary investigations. Interestingly, the authors did not validate their new cut-offs in patients with pituitary disease-causing hyperprolactinaemia.We recently published the utility of cannulated prolactin testing in a cohort of 55 females of reproductive age referred to our institution (Royal Victoria Infirmary, Newcastle upon Tyne, UK) with mild hyperprolactinaemia (< 10 × ULN) on repeat random sampling [2]. All patients were referred following primary care physician review with either symptoms of hyperprolactinaemia or other symptoms prompting a serum prolactin check. Serum prolactin concentrations were measured by sandwich immunoassay using the Roche Prolactin II immunoassay (Roche Diagnostics). The prolactin reference range for females used in our laboratory is manufacturer-defined (102−496 mIU/L or 4.8−23.3 ng/mL). We re-analysed the referral prolactin concentrations in our cohort to investigate the performance of the newly proposed ULN (37.8 ng/mL or 804 mIU/L) for females.