Inhibin B – hormone analysis in fertility studies
Inhibin is a hormone that is produced in the gonads and has an important role in regulating the body's reproductive system. In men, the hormone is produced primarily by the Sertoli cells in the testicles and is closely linked to sperm production. In women, inhibin B is mainly produced by granulosa cells in the ovarian follicles and can provide information about follicular activity.
The analysis measures the concentration of Inhibin B in serum and is used for specific questions related to fertility, spermatogenesis and gonadal function.
Inhibin B is part of the body's feedback system between the gonads and the pituitary gland. The hormone inhibits the release of FSH (follicle-stimulating hormone), and can therefore provide information about how the hormonal and reproductive function of the testicles and ovaries works.
An analysis of S-Inhibin B may be relevant, among other things, in:
- investigation of male infertility.
- assessment of sperm production and spermatogenesis.
- assessment of the function of Sertoli cells in the testicles.
- suspected impaired gonadal or testicular function.
- supplementary assessment of ovarian function in women.
Inhibin B - Function in men
In men, Inhibin B is primarily a marker for the function of Sertoli cells and spermatogenesis, i.e. the formation and development of sperm. A low value may occur in cases of impaired sperm production or effects on the sperm-producing part of the testicles.
The analysis can therefore provide valuable supplementary information in male fertility investigations. However, Inhibin B does not replace a semen analysis and a single value cannot determine whether a person is fertile or infertile. The result is often assessed together with, for example, FSH, LH and testosterone.
Inhibin B in women
In women, Inhibin B is produced in the growing follicles in the ovaries. The level can therefore provide information about follicular activity and ovarian function. Inhibin B can be used as a supplementary analysis in fertility investigations, but when assessing ovarian reserve, AMH is today often a more established marker. Inhibin B can still provide information in certain specific clinical situations.
When can an Inhibin B blood test be justified?
Inhibin B is not a general hormone test but a more specialized analysis. The test may be justified when there is a specific question about fertility, sperm production, testicular function or ovarian function. The analysis can also be used in specialist care for certain other conditions, for example in the investigation of gonadal function and in the diagnosis or follow-up of certain granulosa cell tumors.
How are the results interpreted?
Inhibin B needs to be interpreted based on factors such as gender, age and the current medical issue. In women, the level is also affected by reproductive status and menstrual cycle. A high or low value is therefore not diagnostic in itself. The result needs to be assessed together with other hormone tests and other clinical findings.
Reference interval for Inhibin B
The reference interval for S-Inhibin B varies depending on gender, age and reproductive status. The result is given in ng/L.
- Women of childbearing age: < 340 ng/L
- Women after menopause: > 10 ng/L
- Men: 25–325 ng/L
In women, the level of Inhibin B can also vary during the menstrual cycle. The reference interval also depends on the analysis method, which means that the result should always be assessed against the reference interval stated on the current laboratory result.
Important before taking a sample of Inhibin B
S-Inhibin B is a special analysis performed by the Karolinska University Laboratory. The sample can therefore only be taken at sampling clinics that are affiliated with the Karolinska University Laboratory. When booking, only clinics where the analysis can be performed will be available for selection.
The analysis is only performed 1-2 times per month, which means a limited analysis frequency. This means that the response time may be longer than for regular hormone tests, at least 15 working days.
