Correlation of Nb2 bioassay and radioimmunoassay values for human serum prolactin

The availability of a sensitive and specific bioassay (BA) for PRL in human serum has made possible a comparative assessment of PRL bioactivity and immunoactivity in normal and abnormal serum specimens. Serum was studied from 20 normal subjects and 54 patients with a variety of disorders relating to PRL secretion. The correlation between the results of both assays was very close in all subjects. The mean BA/RIA ratio in normal subjects was 0.90, with a range from 0.67-1.33, and in patients with disordered PRL secretion the mean BA/RIA ratio was 0.94, with a range from 0.53-1.58. Similar results were obtained with PRL stimulatory testing using TRH, metoclopramide, and domperidone, and samples of culture medium from both PRL-secreting and non-PRL-secreting human pituitary tumor cultures. In one patient with a high proportion of "big, big" PRL and hyperprolactinaemia a BA/RIA ratio of 2.47 was found, a value well outside the normal range. However another patient with a similar history had a ratio of 0.82, in the range observed in normal subjects. These findings indicate that in a wide variety of clinical disorders the correlation between PRL bioactivity in the Nb2 system and immunoactivity in human serum samples is remarkably good under basal and stimulated conditions. One exception was found, but the nature of the underlying PRL abnormality in this patient remains to be investigated.