Establishment of reference values for endocrine tests II: Hyperprolactinemia

Background: In patients with hyperprolactinemia, the thyrotropin-releasing hormone (TRH) stimulation test is widely applied to distinguish prolactinom a from other causes of hyperprolactinemia, In the present study, we establi shed reference values for the plasma concentration of prolactin (PRL) and i ts response to TRH. Methods: Basal PRL and the PRL response to 400 mu g TRH iv was determined i n 50 subjects recruited from the general population, equally distributed ac cording to sex and age between 20 and 69 years. PRL was determined by a flu oroimmunometric assay. Reference values are given as the observed range. Results: Plasma concentrations of PRL were 4.0-25 mu g/l (median: 10.0 mu g /l) in women and 0.5-19.0 mu g/l (median: 8.5 mu g/l) in men (p = 0.11). Th e peak PRL concentration after stimulation with TRH was slightly higher in women (median: 51 mu g/l) than in men (median: 41 mu g/l; p = 0.04) and was reached at t = 20 min in all subjects. The relative increase in plasma PRL (median: 440%) did not show a statistically significant effect of age or s ex. In 12 subjects (24%), the relative increase in plasma PRL was lower tha n 250%, which has traditionally been considered the minimum cutoff for a no rmal response. There were no effects of smoking and alcohol, but regular in gestion of liquorice was associated with lower basal (p = 0.03) and lower s timulated (p = 0.05) plasma concentrations of PRL. Conclusions: The present study provides reference values for basal and TRH- stimulated plasma concentrations of PRL. (C) 1999 Elsevier Science B.V. All rights reserved.