Inhibin B: A better infertility marker than FSH or LH?

"Approximately 15% of couples in the world are infertile, and almost 30% of this is due to male factor infertility," said lead author Ashok Agarwal, PhD, director of the andrology clinical and research laboratories at the Cleveland Clinic. "Traditionally, FSH and LH are used to distinguish the peripheral and central causes of male infertility. However, the diagnostic accuracy of FSH was questioned due to a wide overlap of FSH levels in regular and reduced spermato-genesis states. It emphasizes the need for a better marker of male infertility."

To determine whether inhibin B might be a better marker for infertility than FSH or LH, Dr. Agarwal and colleagues assessed serum levels of inhi-bin B, LH, FSH, testosterone, and prolactin in 75 men with fertility problems lasting 12 to 96 months and 12 men with proven fertility. Their semen also was analyzed, and their testicular volumes measured.

While there is evidence that inhibin B can be used as a marker for male infertility, he added, it remains unclear whether it is a better marker than FSH.

Comparing inhibin B and FSH

Both mean inhibin B and testosterone levels were significantly lower in patients with fertility problems, compared with fertile controls (116.4 vs 181.2 pg/mL, p=.008 for inhibin B; and 13.6 vs 24.1 nmol/L, p=.0008 for testosterone, respectively). FSH, LH, and prolactin levels were higher in patients with fertility problems than in fertile controls, but none of these differences approached statistical significance.

Testicular volume, sperm count, and sperm motility all positively correlated with inhibin B and negatively correlated with LH and FSH. However, these correlations were stronger for inhibin B than they were for FSH. Inhibin B also negatively correlated with FSH and LH and positively correlated with testosterone level, which demonstrates a primary interaction among these markers.

"Inhibin B levels could be a better marker for assessment of male fertility status than FSH and LH," Dr. Agarwal said. "Inhibin B levels in patients with infertility may provide useful information on spermatogenesis and possibly serve as a more direct marker of the spermatogenesis than FSH. [It] can also serve as a useful marker of spermatogenesis in patients with vari-coceles, cryptorchidism, etc."

Clinically, Dr. Agarwal said inhibin B could be measured following the measurement of testosterone.

"If the level of inhibin B is within normal limits, then it is unlikely to be a testicular pathology," he said. "Subsequently, the levels of FSH and LH could be determined. Since inhibin B is a direct marker of spermatogenesis, it would be useful for formulating new therapeutic methods in the evaluation and treatment of male infertility."

Dr. Agarwal warned, however, that these findings must be verified in different groups of patient populations before generalizations can be made. The results also require validation via large-scale, multicenter, prospective trials.

"Inhibin B/FSH index seems to correlate with the inhibin B level," he added. "Future prospective studies are essential to define the significance of these indices in male infertility evaluation."