What is Inhibin?

Inhibin is an endocrine hormone produced in the ovaries and the testes. This hormone has several functions in the body, with levels in women being linked to the menstrual cycle and playing a role in fetal development. Another hormone, activin, has an action in the body opposite to that of inhibin. Levels of these two hormones tend to fluctuate in both men and women in response to a number of cues, which can include changes in hormone levels triggered by natural biological processes, environmental pressure, and other factors.

Two different inhibin complexes are recognized: A and B. In women, levels of the first tend to peak around the mid-luteal phase, while the second peaks twice, in mid-follicular phase and again during ovulation. As with other endocrine hormones, the levels of this hormone can be influenced by other hormones. The endocrine system is maintained in a state of delicate balance, and a small change can set up a chain reaction with far-reaching consequences.

When this hormone is secreted, it inhibits the production of follicle-stimulating hormone (FSH) and the release of gonadotropin-releasing hormone. This plays a vital role in the menstrual cycle, in which both of these hormones are involved, and it can also be involved in fertility. Fertility testing can include an assessment of levels of this hormone along with other hormones in the body to learn more about the reasons for infertility.

Levels of Inhibin A are routinely checked during a quad screen, a basic blood test performed to check for abnormalities in a pregnancy. If the levels are high, it can indicate that the developing fetus may have chromosomal abnormalities. Abnormal results should not be taken at face value, however; a medical professional needs to perform follow up tests to learn more about the situation. It may be that there is no problem with the developing fetus, and that the abnormal results were a fluke.

When a test of this hormone is ordered, blood will be collected from the patient and analyzed. The test is not very painful, although the experience of having blood drawn can be unpleasant, and it carries very low risks. The time it takes for test results to be returned varies, depending on the lab facilities used to analyze the blood; if blood needs to be shipped out for analysis or the lab is busy with work, it can take several days.