The evaluation of pharmacological somatotropic tests and their interpretation are still controversial. Recently, it has been suggested that estrogen priming would allow for a better distinction between normal and pathological populations. Defining a cutoff line for normality is problematic; therefore, in this preliminary paper, we decided to critically consider this aspect in a prepubertal population. Fourteen prepubertal subjects (O = 2 and O= 12) with a chronological age range between 5-12,3 years, bone age between 5,2-11,5 years, height more than -2SDS, growth velocity ≥ 10th percentile and normal weight were evaluated. All subjects underwent two clonidine tests(100μg/m2) with GH measurements (IRMA): at baseline (B), 60, 90 and 120 min., one receiving placebo (P) and another receiving estradiol (E), 0.5 mg/m2 orally for the previous 3 days. The sequence of tests was random, double blind and with a six-week interval. For the statistical comparison between basal levels and maximal responses in both groups the Wilcoxon test (Signed rank test) was used. Results obtained (median and range) were: B GH (ng/ml), with P= 0.53 (0.4-2.50) and with E = 0.97 (0.4-2.00), (p=NS) and Mx GH (ng/ml), with P = 19.0 (7.8-33.0), with E = 24.5 (12.0-50.0), (p>0.002). Estradiol levels were () with P and () with E. In two cases with P responses below 10 ng/ml were observed while all children with E had responses above this value.

Conclusions: 1- Most children had responses above 10 ng/ml, without previous priming. Those who were not responsive“normalized” their response with E.

2-These being children with normal height and growth velocity, should the cutoff lines currently used be redefined?

3-Should different “normality” criteria be established depending on the stimulation test when priming is used?

4-From our experience, when estradiol is used, the dose should be adjusted according to the body surface area.