Estrogen priming effect on growth hormone (GH) provocative test:: A useful tool for the diagnosis of GH deficiency

We have studied the effect of estradiol (E-2)on the GH-insulin-like growth factor (GH-IGF) axis in 15 prepubertal GH deficiency (GHD) children and 44 prepubertal or early pubertal children with idiopathic short stature (SS). All of them received a daily dose of micronized E-2 (1 or 2 mg) or placebo, for 3 days, before a sequential arginine-clonidine test. In SS children, GH maximal responses were 17.8 +/- 10.9 on placebo and 27.9 +/- 14.5 mug/L on estrogen (P < 0.0001). The lower 95% confidence limits for GH maximal response changed from 3.7 <mu>g/L (without E-2) to 8.3 mug/L (on E-2). In GHD children, no significant stimulatory effect of estrogen on GH levels was observed. After placebo, a cut-off limit of 3.7 mug/L (the lower 95% confidence interval limit) resulted in 73% sensitivity, 95% specificity, and an overall 90% diagnostic efficiency. After E-2, a cut-off limit of 8.3 mug/L resulted in a sensitivity of 87%, a specificity of 98%, and a diagnostic efficiency of 95%. After placebo, 68% of SS showed normal IGF-I levels, and the mean did not change on E-2 (13.7 +/- 6.3 vs. 14.3 +/- 6.8 nmol/L, not significant). In 93% of SS, IGF binding protein (IGFBP)-3 levels were normal during placebo. On E-2, mean IGFBP-3 did not change (2.63 +/- 0.70 vs. 2.70 +/- 0.70 mg/L, not significant). In 14 of 15 GHD patients, IGF-I values were below normal on placebo, and the mean of the group did not change after E-2. During placebo, 13 of 15 GHD children presented low IGFBP-3 values. During E-2, there was a small significant increase in IGFBP-3 values (1.06 +/- 0.58 vs. 1.20 +/- 0.69 mg/L, P < 0.02). The highest diagnostic efficiencies for IGF-I and IGFBP-3 were observed during placebo (75% and 91%, respectively). We conclude that GH stimulation tests after E-2 priming had the highest diagnostic efficiency. Our findings suggest that the effect of estrogen priming on GH stimulated levels, by reducing the number of false nonresponders, might be useful to better discriminate between normal and abnormal GH status in SS children.