Inhibin B: A Reliable Marker of Sperm Production

Understanding Inhibin B and Male Fertility

Inhibin B is a peptide hormone secreted primarily by Sertoli cells in the seminiferous tubules of the testes. It plays a critical role in the regulation of the hypothalamic-pituitary-gonadal (HPG) axis and serves as a negative feedback signal to the anterior pituitary to suppress follicle-stimulating hormone (FSH) secretion. Clinically, inhibin B has emerged as a valuable biomarker for assessing spermatogenic activity and testicular function in men.

The Physiology Behind the Marker

Inhibin B levels in adult males reflect the functional state of Sertoli cells and, by extension, active spermatogenesis. Sertoli cells support and nourish developing germ cells, and their capacity to produce inhibin B is directly linked to the number and maturity of spermatogenic cells. When spermatogenesis is impaired—due to genetic, endocrine, or toxicologic causes—serum inhibin B levels typically decline.

Conversely, when spermatogenesis is intact and efficient, inhibin B concentrations are within the normal reference range. This feedback is useful for assessing the testicular response to FSH and for evaluating testicular reserve and fertility potential.

Correlation with Sperm Count

Several studies have shown a positive correlation between serum inhibin B levels and total sperm count, sperm concentration, and motility. Low inhibin B levels are often associated with oligospermia (low sperm count) or azoospermia (absence of sperm), especially of non-obstructive origin. This makes inhibin B an especially valuable test when semen analysis is inconclusive or impossible.

In a clinical setting, serum inhibin B < 80 pg/mL often suggests significant impairment in spermatogenesis, while levels > 150 pg/mL generally support normal sperm production. The inhibin B-to-FSH ratio may further increase diagnostic sensitivity, especially in distinguishing between primary testicular failure and secondary hypogonadism.

Clinical Uses

• Male infertility workup: Inhibin B is used to evaluate men with subfertility or infertility, particularly those with abnormal semen parameters or unexplained infertility.
• Non-obstructive azoospermia (NOA): Inhibin B helps differentiate between obstructive and non-obstructive causes, which has implications for testicular biopsy or sperm retrieval procedures.
• Monitoring fertility recovery: After gonadotoxic exposures (e.g., chemotherapy), inhibin B can help monitor the return of spermatogenesis.
• Adolescents and delayed puberty: Inhibin B levels may assist in evaluating testicular development and predicting the onset of spermatogenesis.

Advantages Over Other Markers

Compared to testosterone or FSH, inhibin B is more directly reflective of seminiferous tubule activity. While FSH rises in response to impaired spermatogenesis, it is not a direct indicator of active sperm production. Testosterone levels may remain normal even in the absence of spermatogenesis because they reflect Leydig cell activity. Inhibin B, by contrast, comes from Sertoli cells and tracks closely with the process of sperm development itself.

Limitations and Considerations

Inhibin B testing is not without limitations. Values can vary with assay methods, age, BMI, and diurnal rhythm (levels are higher in the morning). While helpful, inhibin B should be interpreted alongside a complete clinical picture, including semen analysis, hormone panel (FSH, LH, testosterone), and possibly scrotal ultrasound.

In men with Klinefelter syndrome or maturation arrest, inhibin B is often undetectable. However, very low levels do not absolutely rule out the presence of sperm retrievable by testicular sperm extraction (TESE), so clinical decisions should not rely solely on inhibin B levels.

Summary

Inhibin B is a direct, non-invasive marker of active spermatogenesis that provides valuable insight into male fertility. It correlates well with sperm count and testicular function and is particularly useful in complex fertility cases or when semen analysis is not feasible. At The Performance Medicine Institute, we incorporate inhibin B testing into our advanced fertility evaluations to deliver accurate, actionable insights for men pursuing family-building goals.

If you’re concerned about fertility or considering a fertility assessment, contact us to schedule a personalized evaluation with our team.

References

Grinspon RP, Rey RA. Regulation of Sertoli cell development by FSH and androgen during different stages of life. Front Endocrinol (Lausanne). 2019;10:261.

Pierik FH, Vreeburg JT, Stijnen T, de Jong FH, Weber RF. Serum inhibin B as a marker of spermatogenesis. J Clin Endocrinol Metab. 1998;83(11):3826–32.

Mahmoud AM, Comhaire FH, Abdel-Rahman AH. The role of inhibin B in the diagnosis of male infertility. Hum Reprod. 2000;15(3):535–40.

Meachem SJ, Nieschlag E, Simoni M. Inhibin B in male reproduction: pathophysiology and clinical relevance. Eur J Endocrinol. 2001;145(5):561–71.