Clinical Use: Testing for inhibin can be used as an aid in the diagnosis of granulosa cell tumours and mucinous epithelial ovarian tumours. It can also be used as an aid in assessing infertility issues.
Background: Inhibins are heterodimeric protein hormones secreted by granulosa cells of the ovary in females and Sertoli cells of the testis in males. Inhibins selectively suppress the secretion of pituitary follicle-stimulating hormone (FSH). The inhibins consist of a dimer of 2 homologous subunits, an alpha subunit and either a beta A or beta B subunit, to form inhibin A and inhibin B, respectively.

In females, inhibin A is primarily produced by the dominant follicle and corpus luteum, whereas inhibin B is primarily produced by small developing follicles. Serum inhibin A and B levels fluctuate during the menstrual cycle. Inhibin A is low in the early follicular phase and rises at ovulation to maximum levels in the midluteal phase. In contrast, inhibin B levels increase early in the follicular phase to reach a peak coincident with the onset of the midfollicular phase decline in FSH levels. Inhibin B levels decrease in the late follicular phase.

Elevations of serum inhibin A and/or B are detected in some patients with granulosa cell tumours. Inhibin B elevations have been reported in 89% to 100% of patients with granulosa cell tumours. In those patients, inhibin B levels tend to be elevated about 60-fold over the reference range value. Inhibin B also appears to be a suitable serum marker for epithelial tumours of the mucinous type with about 55% to 60% having elevated inhibin B levels. In contrast, inhibin is not a very good marker in nonmucinous epithelial tumours. At best, total inhibin is elevated in 15% to 35% of nonmucinous epithelial ovarian cancer cases.

With respect to infertility investigations Inhibin B levels can be used to assess ovarian reserve and it is suggested that levels can also predict the success of ovulation-inducing drugs e.g Clomid. It is usual to take a blood sample for Inhibin on day 3 of the cycle – women with unexplained fertility and those over 35 years old are said to benefit from this investigation.

Reference Ranges: Adult Males: 25 – 325 ng/L
Adult Females: < 341 ng/L
Adult Females Day 3 of cycle: Post-menopausal: < 5 ng/L
Associated Diseases:
Patient Preparation: None

Note that if the patient is being investigated for infertility a blood sample should be taken on day 3 of the menstrual cycle.

Specimen Requirements: SERUM (Plain Red top or SST)
Turnaround Time: 4 weeks
Additional Information: For aid in diagnosis, follow-up, re-occurrence indicator of ovarian granulosa and mucinous tumours. Note that only B type is measured. When measured in infertility studies i.e. to assess ovarian reserve/ suitability for IVF, sample should be taken on day
Referred Test: Referred test
Location: Charing Cross Hospital