Inhibin B Test

Inhibin B test is one of the laboratory tests conducted to diagnose female infertility. Inhibin B plays an important role not only in the female body – its concentration is also important for male fertility.

Together with AMH (anti-Müllerian hormone), inhibin B belongs to the main diagnostic group for assessing female fertility. This hormone, along with the AMH indicator, is one of the most important parameters for evaluating ovarian reserve. Determining the concentration of inhibin B allows not only to assess the number and quality of oocytes but also to predict the response to ovarian stimulation during assisted reproduction procedures.

In both women and men, inhibin B concentration decreases with age, which is usually accompanied by an increase in FSH (follicle-stimulating hormone) concentration. A decrease in inhibin B is an early sign indicating a reduction in follicle numbers as the reproductive system ages. This marker is also important in studies examining the relationship between uterine removal surgery and the risk of early ovarian failure.

In older women, inhibin B concentration in the blood is about 20% lower, while FSH and estradiol concentrations are higher. This indicates that weakened negative feedback of inhibin B is one of the main factors leading to the early increase in FSH concentration during the aging process.

Indications for Inhibin B Test

The test is conducted for women to:

• assess fertility;
• plan pregnancy, especially if childbirth is delayed for several years – determining inhibin B concentration helps assess the number of follicles that can mature into valuable oocytes;
• determine the causes of pregnancy failures;
• assess the possibility of conceiving at an older age;
• predict the effectiveness of ovarian stimulation in cases of assisted reproduction (e.g., in vitro procedures).

The test is conducted for men to:

• assess spermatogenesis;
• determine the functionality of testicular seminiferous tubules;
• monitor the results of treatment for hypogonadotropic hypogonadism;
• make decisions regarding testicular biopsy or varicocele surgery.

Preparation for the Test

No special preparation is needed. For women, it is recommended to test inhibin B levels during the follicular phase, preferably on the third day of the menstrual cycle. Depending on the test's purpose, the doctor may choose another day of the cycle.

Interpretation of Results

Increased concentration
A very high level of inhibin B may indicate ovarian tumors. In such cases, it is necessary to consult a specialist doctor.

Decreased concentration in women may indicate:

• decreased ovarian reserve (natural during menopause);
• premature ovarian failure;
• resistant ovary (Savage) syndrome;
• hypothalamic dysfunction.

Decreased concentration in men may indicate:

• azoospermia (absence of sperm in ejaculate);
• Sertoli cell syndrome;
• damage to testicular seminiferous tubules;
• germ cell arrest;
• development of germ cell tumors;
• Kallmann syndrome;
• Klinefelter syndrome.