Inhibin B, produced by Sertoli cells in males and granulosa cells in females, provides negative feedback to the anterior pituitary to suppress follicle-stimulating hormone (FSH) secretion. It helps regulate spermatogenesis and folliculogenesis, reflects Sertoli-cell function and ovarian reserve, and counterbalances activin signaling to fine-tune gonadal hormone production and germ-cell development.

Inhibin B high levels usually reflect active ovarian or testicular function. In men, high inhibin B generally indicates good spermatogenesis or a positive response to fertility treatment. In women, levels rise with follicular activity, but markedly elevated values can suggest granulosa‑cell or other ovarian tumors. Abnormal elevations require clinical correlation, repeat testing and imaging or specialist referral to exclude hormone‑secreting pathology.

An inhibin B test measures blood levels of inhibin B, a hormone made by ovarian granulosa cells in women and Sertoli cells in men. It helps assess ovarian reserve and predict response to fertility treatment in women, and evaluates spermatogenesis and male infertility. It’s used alongside other reproductive hormones (FSH, LH, AMH) to diagnose and monitor pituitary–gonadal function and fertility issues.

Inhibin A and inhibin B are gonadal glycoproteins that suppress pituitary FSH. Inhibin B is produced mainly by ovarian granulosa cells in the follicular phase and by testicular Sertoli cells, reflecting ovarian reserve and spermatogenesis. Inhibin A is produced primarily by luteal granulosa cells and the placenta (especially in pregnancy) and is used clinically in luteal-phase assessment and prenatal screening; levels vary across the cycle.

Low inhibin B reflects impaired Sertoli- or granulosa-cell function and reduced gonadal reserve. Causes include advancing age/menopause, primary ovarian insufficiency or diminished ovarian reserve, ovarian surgery, chemotherapy/radiation, and hormonal suppression (combined oral contraceptives, GnRH analogues). In men it follows testicular damage—torsion, orchitis, varicocele, cryptorchidism, Klinefelter syndrome, toxin exposure—or pituitary/hypothalamic hypogonadism.

Normal inhibin B varies with age and cycle. In reproductive‑age women values typically range roughly 20–300 pg/mL; follicular‑phase values are often about 20–200 pg/mL with midcycle peaks higher. Postmenopausal levels are low, commonly <20 pg/mL. Reference ranges differ by laboratory and assay, so clinicians interpret results alongside other ovarian‑reserve markers and the clinical context.