Evaluation of basal sex hormone levels for activation of the hypothalamic-pituitary-gonadal axis

Background: This study aimed to identify the predictive value of basal sex hormone levels for activation of the hypothalamic-pituitary-gonadal (HPG) axis in girls. Methods: Gonadotropin-releasing hormone (GnRH) stimulation tests were performed and evaluated in a total of 1750 girls with development of secondary sex characteristics. Correlation analyses were conducted between basal sex hormones and peak luteinizing hormone (LH) levels >= 5 IU/L during the GnRH stimulation test. Receiver operating characteristic (ROC) curves for basal levels of LH, follicle-stimulating hormone (FSH), LH/FSH, and estradiol (E2) before the GnRH stimulation test were plotted. The area under the curve (AUC) and 95% confidence intervals (CIs) were measured for each curve. Results: The maximum AUC value was observed for basal LH levels (0.77, 95% CI: 0.74-0.79), followed by basal FSH levels (0.73, 95% CI: 0.70-0.75), the basal LH/FSH ratio (0.68, 95% CI: 0.65-0.71), and basal E2 levels (0.61, 95% CI: 0.59-0.64). The appropriate cutoff value of basal LH levels associated with a positive response of the GnRH stimulation test was 0.35 IU/L, with a sensitivity of 63.96% and specificity of 76.3% from the ROC curves when Youden's index showed the maximum value. When 100% of patients had peak LH levels >= 5 IU/L, basal LH values were >2.72 IU/L, but the specificity was only 5.45%. Conclusions: Increased basal LH levels are a significant predictor of a positive response during the GnRH stimulation test for assessing activation of the HPG axis in most girls with early pubertal signs.