Contribution to the problem of hyperprolactinaemia: experience with 4,199 prolactin assays and 117 prolactinomas

To help define the normal and pathological serum prolactin concentration ranges in adult females.

Serum prolactin was assayed in a mixed population of 4,199 women divided into five groups: (A) 753 with normal menses consulting for infertility (control group); (B) 2,523 with menstrual disorders; (C) 519 with hirsutism and normal cycles; (D) 201 with galactorrhoea and normal cycles; (E) 203 with galactorrhoea and menstrual disorders.

In each group, a separate subset (2%, 3%, 1%, 15%, and 42.3%, respectively) was distinguished, with scattered prolactin values above 30 ng/mL, in which 117 prolactinomas were found, with an incidence ranging from 11 to 57% in cases with prolactin of 31-49 ng/mL and from 65 to 87.5% in those with prolactin > or = 50 ng/mL. The frequency distribution of values from 1 to 30 ng/mL was strikingly similar in the 753 subjects of group A and the 2,523 patients of group B: 91% and 92.6%, respectively, between 1 and 15 ng/mL, and 5.5% and 4.7% from 16 to 20 ng/mL. Values > 20 ng/mL were found in 4.4% of the subjects in group A, 5.5% in group B, 5.1% in group C, 21.8% in group D, and 18.7% in group E.

(a) Normal prolactin values can be considered to include 1-15 ng/mL and 16-20 ng/mL, the former corresponding to the vast majority of normal subjects or patients, and the latter being the extreme limit of normal, for which from a clinical point of view repetition of the assay and a follow-up is advocated. (b) Values between 21 and 30 are rare and could be considered as hyperprolactinemia necessitating further investigation. (c) Values between 31 and 49 are suspect, and values > or = 50 ng/mL are suggestive of the presence of a prolactinoma, warranting thorough investigation.