Basal prolactin and total lactogenic hormone levels by microbioassay and immunoassay in normal human sera

The availability of an improved microbioassay for prolactin measurement has enabled comparison of lactogenic hormone bioactivity and immunoreactivity in normal human serum. Serum was studied from 61 normal females and 15 normal males. The correlation of both assays was very close for all subjects with a mean ratio of bioassay to immunoassay of 1.5 (range 0.8-2.0) for prolactin and 1.4 (range 0.5-1.9) for total lactogenic hormone. There was no significant variation in prolactin or total lactogenic hormone values by microbioassay or immunoassay with sexual or menstrual status. Postmenopausal prolactin levels were lower by both assays compared with premenopausal values with a relative and absolute decrease in prolactin bioactivity with age. These findings indicate that there is a good correlation between prolactin bioactivity and immunoactivity in human serum.