Inhibin B.

Inhibin B is a protein hormone that plays some important roles in the human body, especially when it comes to fertility. Testing its concentration is one element in the diagnosis of infertility. What is this hormone responsible for and how to prepare for the test?

What is inhibin B?

Inhibin B[1] is one of the protein hormones, the concentration of which affects women's ability to conceive. It is produced by so-called granulosa cells found in the ovarian follicle, as well as by the pituitary gland and, during pregnancy, by the placenta.

In the female body, inhibin stimulates the ovaries to synthesise oestrogen and influences the normal regulation of the menstrual cycle.

The concentration of this hormone is not constant and the its secretion varies during the menstrual cycle women. Physiologically, inhibin B levels rise around day 3 to 5 of the cycle, to fall in the late follicular phase and then rise sharply just before ovulation.

In a man's body Inhibin B is produced in the testes by so-called Sertoli cells. Adequate levels of this hormone have a significant effect on spermatogenesis and the normal function of the testes. For this reason, inhibin B testing belongs to the panel of diagnostic tests for male infertility[1].

In both men and women, inhibin is also responsible for inhibiting the synthesis of FSH by the pituitary gland, affecting the regulation of gamete maturation in both sexes.

There is another type of inhibin in the body - it is inhibin Awhich has a slightly different chemical structure from inhibin B. Testing its concentration not only helps in the diagnosis of infertility (especially female infertility), but when performed during pregnancy can be an important indicator in assessing the risk of pregnancy abnormalities. Assessment of inhibin A levels in pregnant women is carried out especially in those who have already had problems with a normal pregnancy or are at risk.

Inhibin B - when to test?

Inhibin B testing is most commonly performed in women for diagnosis of reproductive health abnormalities. The examination should be performed by patients in whom symptoms such as:

  • difficulties in getting pregnant,
  • irregular menstruation,
  • premature signs of menopause.

In women preparing for an IVF procedure or a insemination inhibin B testing is one of the tests that can accurately (indirectly) assess the ovarian reserve (next to AMH tests) and determine the success of hormonal ovarian stimulation[1][2].

In men, inhibin B is determined for assessment of spermatogenesisand to monitor the correct treatment of hypogonadotropic hypogonadism. Determining its level is also an important indicator in deciding whether to perform a diagnostic testicular biopsy or to perform surgery for varicocelectomy[1].

Testing for inhibin B levels is performed from a venous blood sample taken from the patient. No preparation is needed for it. It is also not necessary to be fasting.

How to read the results?

In women, the result of the inhibin B test depends on their age and also on the phase of the cycle in which the material for the test was taken. Reference values are as follows[1]:

  • Day 1 and 2 of the menstrual cycle: 15-70 pg/ml,
  • From day 3 to day 5 of the menstrual cycle: 45-120 pg/ml,
  • late follicular phase: 30-90 pg/ml,
  • during ovulation: 80-200 pg/ml,
  • luteal phase: <50 pg/ml,
  • during the menopause: <10 pg/ml.

A result above 45 pg/ml on day three of the cycle indicates a normal ovarian reserve.

In men, normal values for the hormone concentration should be in the range of 120 to 400 pg/ml[1].

Increased levels of this hormone in women, especially when significant, may indicate the presence of ovarian tumours (granulomas). At smaller deviations from normal, they may indicate that the patient has polycystic ovary syndrome.

In the case of underperformancein a woman ailments such as the following may be suspected[1]:

  • Turner syndrome,
  • a decrease in ovarian reserve or premature cessation of ovarian function,
  • the occurrence of refractory ovarian syndrome (so-called Savage syndrome),
  • hypothalamic secretory dysfunction.

It is important to note that inhibin B levels drop significantly in the period immediately preceding menopause. Therefore, in patients over 40 years of age, the reduction in hormone levels is considered physiological.

In the case of men too low inhibin B may indicate:

  • azoospermia (absence of sperm in the semen),
  • damage to the seminal tubules of the testis,
  • germ cell retention,
  • Kallman's syndrome,
  • Klinefelter syndrome,
  • the development of germ cell tumours.

Inhibin B - test price

Testing of inhibin B levels is not reimbursed by the National Health Service - neither in women nor in men. The price of a test performed on your own depends mainly on the specific laboratory and its location. The average cost ranges from PLN 160 to 190.

Bibliography:

  1. ENGEL, Jörg B., FELBERBAUM, Ricardo E., REISSMANN, Thomas, et al. Inhibin A/B in HMG or recombinant FSH ovarian stimulation with cetrorelix medication. Reproductive BioMedicine Online, 2001, vol. 3, no. 2, p. 104-108.
  2. LAHLOU, N., BOUVATTIER, C., LINGLART, A., et al. The role of gonadal peptides in clinical investigation. In : Annales de biologie clinique. 2009. p. 283-292.
  3. GEORGES, A., COMMENGES, M., PAPAXANTHOS, A., et al. Intérêt du dosage d'inhibine B dans l'exploration d'une stérilité masculine grave en vue d'AMP. Immuno-analyse & Biologie Spécialisée, 2002, vol. 17, no 3, p. 176-180.
  4. KORABEL, Joanna et KRZYSIEK, Józef. Assessment of ovarian reserve in peri-menopausal women. Menopausal Review, 2013, vol. 12, no 4.
  5. SZAFAROWSKA, Monika et JERZAK, Małgorzata. Oocyte ageing processes and infertility. Ginekol Pol, 2013, vol. 84, p. 298-304.
  6. Ziora, K., Borawska-Dziadek, E., Oświęcimska, J., Świętochowska, E., Ostrowska, Z., Kajdaniuk, D., ... & Małecka-Tendera, E. (2016). Evaluation of serum inhibin B levels in patients with congenital adrenal hyperplasia. Pediatric Endocrinology/Endocrinology, 15(3).