Serum inhibin B in combination with serum FSH is a more sensitive marker than serum FSH alone of impaired spermatogenesis in men, but cannot predict the presence of sperm in testicular tissue samples.

The measurement of serum FSH is useful in the diagnostic workup of the infertile male, but fails to predict the presence of sperm in testicular tissue. We investigated whether inhibin B reflects testicular morphology and the presence of sperm more accurately than FSH. Serum inhibin B and gonadotropin levels were determined in 91 infertile men undergoing diagnostic bilateral testicular biopsy. In 52 of the 91 patients multiple samples were taken for testicular sperm extraction (TESE). Inhibin B levels were (mean ± SEM) 238 ± 32 pg/mL in men with normal spermatogenesis (n = 9), 102 ± 18 pg/mL in men with spermatogenetic arrest (n = 15), 98 ± 16 pg/mL in hypospermatogenesis (n = 23), 41 ± 6 pg/mL in focal Sertoli cell-only syndrome (SCO; n = 26), and 27 ± 8 pg/mL in complete SCO (n = 18). The percentage of SCO tubuli was more strongly correlated to serum inhibin B (r = -0.58; P < 0.01) than to FSH (r = 0.34; P < 0.05). Similarly, the percentage of tubules with elongated spermatids was significantly (P < 0.05) more strongly correlated to serum inhibin B (r = 0.65; P < 0.01) than to FSH (r = -0.4; P < 0.01). Thus, inhibin B is slightly more sensitive than FSH as an index of the spermatogenic status. Neither FSH nor inhibin B alone, however, could predict the type of spermatogenetic damage exactly. The combination of FSH and inhibin B had high diagnostic sensitivity (88%) and specificity (83%) for the presence of elongated spermatids in testicular biopsies. Sperm could be retrieved in 34 (65%) of the TESE patients. The combination of inhibin B and FSH measurement showed a sensitivity of 75% and a specificity of 73% when identifying patients in whom sperm could possibly be retrieved by TESE. We conclude that although the measurement of serum inhibin B improves the sensitivity of predictive tests for the presence of sperm in histology or for TESE, this parameter cannot accurately predict TESE outcome.