What are other Names for this Test? (Equivalent Terms)

• Alpha-Beta A and Alpha-Beta B Blood Test
• Inhibin A and Inhibin B Blood Test

What is Inhibins A and B Blood Test? (Background Information)

• Inhibin A and inhibin B are types of protein that are made by specialized cells in the ovary in females. In males, the Sertoli cells in testis produce inhibin
• Inhibin A and inhibin B levels vary in blood depending on the stage of life and certain specific conditions. Their levels also vary during the menstrual cycle
• Inhibin A and inhibin B levels are very low to virtually undetectable before puberty, premature ovarian failure (POF), and after menopause
• Mutations in the inhibin genes lead to a decrease in the bioactive inhibin. The decreased bioactive inhibin causes loss of suppression of follicle-stimulating hormone (FSH) from the ovaries, resulting in abnormal FSH activity
• Since, FSH is responsible for the normal development and production of ovum in the ovary, a loss of FSH causes premature depletion of follicles, causing premature ovarian failure
• Women with polycystic ovary syndrome (PCOS) have significantly higher concentrations of inhibin A and inhibin B than that of normal women
• Abnormalities in inhibin are also associated with ovarian cancers. Studies have found that certain ovarian tumors, such as granulosa cell tumors (GCTs) and mucinous ovarian tumors, have increased inhibin levels in blood
• The measurement of inhibin levels in blood can have a variety of uses including assessing the health of the developing fetus,  diagnose certain ovarian cancers, and monitor the patient during ovarian cancer treatments
• Inhibin A and inhibin B are released mainly by the fetoplacenta during pregnancy. Inhibin is an important protein in the development of the fetus, specifically in regards to development of the ovary, since both inhibin A and inhibin B regulate the levels of follicle-stimulating hormone (a hormone that is necessary for normal ovarian function). 
• Adequate levels of inhibins A and B are important for the healthy development of a fetus, because of their effects on FSH. Inhibin levels that are too low may indicate a poorly-developing fetus and/or the presence of certain congenital abnormalities
• Inhibin A is the predominant protein in the maternal circulation and measurement of inhibin A in early pregnancy could be predict miscarriage, preeclampsia (pregnancy-induced hypertension), and fetal growth restriction
• The Inhibins A and B Blood Test helps determine the levels of inhibin A and inhibin B in blood. It helps detect abnormalities in menstrual cycle, and consequently, helps diagnose conditions such as premature ovarian failure (POF), endometrial hyperplasia, disordered proliferative endometrium, mid-menstrual cycle stromal breakdowns, and excess menstruation

Along with alpha-fetoprotein (AFP) and unconjugated estriol (uE3), inhibin A and inhibin B levels are also measured as a second-trimester screen for Down syndrome.

What are the Clinical Indications for performing the Inhibins A and B Blood Test?

Following are the clinical indications for performing the Inhibins A and B Blood Test: 

• In women:
  • Investigating possible hormonal-related complications during pregnancy and associated fetal issues
  • Menstrual cycle abnormalities such as premature ovarian failure, endometrial conditions (such as endometrial hyperplasia and disordered proliferative endometrium), mid-menstrual cycle stromal breakdowns, and excess menstruation
  • Family history of Down syndrome
  • Preeclampsia or pregnancy-related high blood pressure
  • Ovarian benign and malignant tumors
• In men, the test may be used as part of workup for fertility issues and to detect sex cord-gonadal stromal tumors

How is the Specimen Collected for Inhibins A and B Blood Test?

Following is the specimen collection process for Inhibins A and B Blood Test:

Sample required: Blood

Process of obtaining a blood sample in adults:

• A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
• The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
• The needle cap is removed and is held in line with the vein, pulling the skin tight
• With a small and quick thrust, the vein is penetrated using the needle
• The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
• The wrap band is removed, gauze is placed on the collection site, and the needle is removed
• The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
• The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Inhibins A and B Blood Test Result?

Interpretations of the Inhibin A and B Blood Test value depend on the maternal age and stage of pregnancy.

• Normal inhibin A values are as follows:
  • Pregnant women: 1.8-97.5 pg/mL
  • Menopausal women: Less than 7.9 pg/mL
  • Men: Less than 2.1 pg/mL
• Normal inhibin B values for women vary according to age:
  • Less than 3 years: Undetectable
  • 3-9 years: Less than 30 pg/mL
  • 10-13 years: Less than 93 pg/mL
  • 14-17 years: Less than 140 pg/mL
  • 18 years to menopause: Less than 255 pg/mL
  • After menopause: Less than 30 pg/mL

The significance of the Inhibins A and B Blood Test result is explained.

• A high value for the test may indicate:
  • Preeclampsia
  • Possibility of a developing fetus with Down syndrome
  • Benign and malignant tumors of the ovary
  • Polycystic ovary syndrome (PCOS)
• A low value for the test may indicate:
  • Premature ovarian aging
  • Premature ovarian failure (POF)

Depending on individual clinical circumstances, the test may help characterize conditions such as endometrial hyperplasia, disordered proliferative endometrium, mid-menstrual cycle stromal breakdowns, and excess menstruation.

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

• Inhibin, produced by granulosa cells in the ovaries of women, is a heterodimeric gonadal glycopeptides consisting of a common a-subunit (alpha-subunit) covalently bonded to a unique b-subunit (beta-subunit) that can be either bA (inhibin A) or bB (inhibin B)

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

Thanks and Gratitude:

We sincerely acknowledge and thank Dr. Jayaprakash Golla for reviewing the article. His valuable input and feedback has helped enrich the contents of this article.

Jayaprakash Golla, PhD
Associate Research Scientist
Department of Environmental Health Sciences
Yale School of Public Health
60 College Street, Rm. 508, PO Box 208034, New Haven, CT 06520-8034, USA