Basal inhibin B and the testosterone response to human chorionic gonadotropin correlate in prepubertal boys

During childhood, the quiescent phase of testicular activity, the hCG stimu lation test is widely used to evaluate testicular function. Inhibin B, a go nadal peptide regulating FSH secretion, is an established marker of Sertoli cell function and spermatogenesis in adults. In contrast to the other horm ones of the hypothalamo-pituitary-gonadal axis, inhibin B is also secreted in detectable amounts during childhood. The aim of this study was to determ ine whether basal inhibin B levels are able to predict prepubertal testicul ar function, so as to avoid a stimulation test. Inhibin B and testosterone before and after hCG stimulation were measured in 54 male children with var ious testicular disorders by an immunoassay specific for inhibin B. Basal i nhibin B was compared to the testosterone increase after hCG. Inhibin B and the hCG-induced testosterone increment correlated strongly (r = 0.84; P < 0.0001). Patients with anorchia were clearly distinguishable from those wit h abdominal testes, having undetectable (inhibin B, < 15 pg/mL) respective normal inhibin B levels for age. Inhibin B and the testosterone response to hCG were low in boys with testicular damage (delayed diagnosis of cryptorc hidism; after testicular torsion) and in patients with gonadal dysgenesis, but were normal or increased in children with androgen insensitivity syndro me. We conclude that basal inhibin B predicts the testosterone response to hCG in boys and therefore gives reliable information about both the presenc e and function of the testes. The diagnostic procedure in cryptorchidism ma y be reduced to a single inhibin B measurement. Furthermore, inhibin B leve ls show specific alterations in patients with sexual ambiguity, adding a va luable diagnostic tool to the complex differential diagnosis of male pseudo hermaphroditism.