Human Chorionic Gonadotropin Stimulation Test in Prepubertal Children with Micropenis Can Accurately Predict Leydig Cell Function in Pubertal or Postpubertal Adolescents

To evaluate the accuracy of the human chorionic gonadotropin (hCG) stimulation test in children with micropenis in predicting later Leydig cell function. Methods: We conducted a retrospective investigation of testosterone response to a 3-day hCG test (3,000 IU/m²/day) in prepuberty to indicate the need for hormone replacement therapy (HRT) in adolescence. Results: Fifty Japanese boys (range, 0.8-15.4 years of age; median, 8.9) with micropenis were enrolled. Thirty-four spontaneously developed puberty and preserved the ability of testosterone production (group 1), while 16 did not develop any pubertal signs without HRT (group 2). Serum testosterone levels after the hCG test (post-hCG T) in group 2 (range, <0.05-1.1 ng/ml; median, 0.24) were significantly lower than in group 1 (range, 0.5-8.7 ng/ml; median, 2.4; p < 0.0001). Based on true positives who required continuous HRT, the area under the receiveroperating characteristics curve for post-hCG T was 0.983 [95% confidence interval (CI), 0.90-1.00]. The post-hCG T cut-off level corresponding to the Youden index was 1.1 ng/ml (95% CI, 1.0-1.1), with a sensitivity of 100.0% (95% CI, 79.4-100.0) and a specificity of 94.1% (95% CI, 80.3-99.3). Conclusions: The hCG test in prepubertal children with micropenis can be useful for predicting Leydig cell function in pubertal or postpubertal adolescents. The post-hCG T cutoff level of 1.1 ng/ml is recommended to screen for those who will likely require HRT for pubertal development.