The Diagnostic Value of Inhibins in Infertility Evaluation

Gillian Lockwood, M.D., Ph.D.

Disclosures

Semin Reprod Med. 2004;22(3) 

In This Article

Inhibin B and the Assessment of the Azoospermic Male Prior to Testicular Sperm Aspiration for Intracytoplasmic Sperm Injection

Inhibin B is the major circulating form of inhibin in the male. Inhibin B is secreted by Sertoli cells in response to FSH and is the major feedback regulator of FSH secretion in man. In the adult, inhibin and activin subunits can be identified within both the Sertoli and Leydig cell populations. Levels of inhibin B in the serum are closely inversely correlated with FSH and may be regarded as a marker of Sertoli cell function. Ezeh et al[64] established that there was a significant difference in FSH levels of azoospermic men in whom surgical sperm retrieval was successful, but an FSH level was not reliably predictive of outcome following testicular sperm extraction (TESE) or testicular biopsy. Assessment of inhibin B levels in men with idiopathic azoospermia or premature testicular failure can, however, identify a group for whom surgical sperm retrieval (TESE /microsurgical epididymal sperm aspiration [MESA]) has a realistic prospect of success notwithstanding their elevated gonadotropin levels.

In a prospective study of more than 100 testicular biopsies of males with a diagnosis of idiopathic or nonobstructive azoospermia,[65] viable sperm suitable for ICSI was retrieved in all patients with an inhibin B level greater than 80 pg/mL irrespective of FSH or testosterone (normal male level for inhibin B = 300 pg /mL) (Fig. 7). In clinical practice, inhibin B may be used to assess all males presenting for reversal of vasectomy, as low levels are predictive of poor fertility outcome, and these couples are counseled to consider percutaneous epididymal sperm aspiration (PESA)/TESE and ICSI in preference to reversal of vasectomy. Bohring and coworkers[66] conducted a study to evaluate the predictive power for sperm retrieval in TESE of inhibin B and FSH levels in conjunction with testicular histology. They concluded that the combination of the two parameters was the best predictor for the presence of sperm, although recognizing that TESE could be successful when both hormones were outside the threshold levels (< 79 pg /mL for inhibin B and >10 mU /mL for FSH). Inhibin B levels can also be used to monitor the response to gonadotropin treatment of azoospermic or severely oligospermic males with hypogonadotropic hypogonadism or following surgery for varicocele.[67]

Figure 7.

(A) Inhibin B levels in azoospermic males undergoing testicular sperm extraction (TESE). (B) Inhibin B versus positive TESE in azoospermic males. FSH, follicle-stimulating hormone.

In summary, the ability to measure inhibin B levels has transformed the diagnostic resources available to the clinician during the fertility consultation. The female patient with a poor prognosis using her own oocytes can be confidently identified and appropriately counseled, and the patients who would otherwise have been excluded from treatment may be encouraged to try. Where the male partner has idiopathic azoospermia or is azoospermic following vasectomy, an inhibin B assessment will contribute to the decision about whether to undergo exploration, biopsy, or vasectomy reversal. Inhibin assessment can also be used to monitor treatment cycles involving ovarian hyperstimulation and accurately predict patients at risk for cycle cancellation due to under- or overresponse. The measurement of inhibin A levels in very early pregnancies achieved using ARTs (in which conventional biochemical markers such as hCG and progesterone may be difficult to interpret) provides direct evidence about the number and viability of the conceptuses.

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