The role of TRH-stimulated prolactin responses in distinguishing gonadotropin deficiency from constitutional delayed puberty.

LHRH and TRH tests were performed in 16 boys age 14.5-18.5 years with constitutional delayed puberty (CDP); 9 idiopathic hypogonadotropic hypogonadism (IHH) males, age 15.0-22.0 years; and 7 control subjects age 14.5-19.5 years. The responses of FSH and LH to LHRH stimulation overlapped so that it was difficult to differentiate IHH from CDP. Some patients with IHH had normal gonadotropin responses. Basal PRL levels were in the normal range in control, IHH, and CDP patients. We found a 6 to 25 times increment or a response of more than 22 ng/ml (normal response) with respect to basal levels in the control group. In the CDP group, we found 2 to 19 fold increments in basal PRL levels after TRH stimulation and the maximum response was more than 22 ng/ml in all the patients. In the IHH group, the increment in basal PRL levels was 2-9 times more after the TRH test and the maximum PRL response was more than 22 ng/ml in 6 of the 9 patients. Although the mean peak responses of PRL to TRH were significantly lower in the IHH group compared to CDP and controls (p < 0.001), the mean peak individual responses in all groups were in the normal range (minimum 2-fold increment) and the responses were more than 22 ng/ml in all cases except 3 of 9 patients in the IHH group. We conclude that PRL response to TRH may help in differentiating CDP from IHH if a "cut off" response level of 22 ng/ml is used.