Inhibin B reference data for fertile and infertile men in Northeast United States

Abstract

OBJECTIVE: To determine normative levels of inhibin B and examine levels in relationship to FSH, sperm count, and motility in a cohort of fertile and infertile men from the Northeast United States. DESIGN: Prospective comparative study of inhibin B levels in fertile and infertile patient groups. MATERIALS AND METHODS: Fertile men were recruited among those presenting for elective vasectomy at a tertiary academic referral center. Men being evaluated for infertility were also recruited within the same practice. Exclusion criteria included current use of hormonal medication, prior vasectomy, and absence of one testicle, unilateral testicular atrophy or hypogonadism. Blood samples were drawn from each participant and inhibin B and FSH levels were measured by immunoassay. Semen parameters were obtained for the infertile group. Descriptive statistics for both fertile and infertile groups were calculated and simple and multiple linear regression analysis was performed to examine the relationship between semen parameters and inhibin B concentration in the infertile group. RESULTS: A total of 56 fertile and 85 infertile men were recruited. The mean serum inhibin B was higher in the fertile group (132 pg/mL) than the infertile group (78 pg/mL, p < 0.001). The 95% CI for inhibin B in fertile men was 114 - 155 pg/ml and 65 - 93 pg/ml for infertile men. The mean FSH levels were 3.5 and 5.6 IU/L for the fertile and infertile groups, respectively (p < 0.001). Inhibin B levels correlated positively (R square = 0.27, p < 0.001) and FSH correlated negatively (R square = 0.33, p < 0.001) with total sperm concentration. General linear model multiple regression demonstrated that the parameters were equally predictive of sperm concentration. This resulted from the high negative correlation between FSH and inhibin (R square = 0.46, p < 0.001). CONCLUSIONS: Inhibin B levels in fertile men were defined and found to be similar, but not identical, to those reported in other geographic regions. Both inhibin B and FSH are useful markers of spermatogenesis in infertile men.