Serum inhibin B as a marker for spermatogenesis

Inhibin B generated by Sertoli cells provides negative feedback on FSH secretion. In men, inhibin B seems to be the physiologically important form of inhibin. Serum inhibin B was measured by two-site immunoenzymatic assay in 40 normal men (27 years of age) with sperm concentrations 100 +/- 9.2 x 10(6)/mL, 51 subfertile men (31 years of age) with sperm concentrations 6.8 +/- 0.8 x 10(6)/mL, 16 men with varicocele with sperm concentrations 54.3 +/- 0.8 x 10(6)/mL (31 years of age), men with hypogonadotrophic hypogonadism, men with Klinefelter syndrome, and men with obstructive and non-obstructive azoospermia. In men with normal sperm concentrations (>20 x 10(6) mL) serum inhibin B was 201 +/- 17 pg/mL and FSH 4 +/- 0.5 IU/L. Varicocele patients showed normal sperm concentrations > 20 x 10(6)/mL, normal serum inhibin B (173 +/- 21 pg/mL), and normal FSH levels (4.6 +/- 0.6 IU/L). In patients with sperm concentrations < 20 x 10(6)/mL the inhibin B level was 118 +/- 14 pg/mL and the FSH level was 10 +/- 1.1 IU/L. In all patients, except those with hypogonadotrophic hypogonadism and Klinefelter syndrome. inhibin B and FSH were inversely correlated (r = -.41, p > 0.01). There was a positive correlation between inhibin B and sperm concentrations (r = .34, p < .01). In varicocele men there was a correlation of r = .574, p < .05. Inhibin B may be a marker of exocrine testicular function and may offer an improved diagnosis of testicular dysfunction.