The serum inhibin B concentration and reference ranges in normozoospermia

Although an inhibin B assay may be useful in the assessment of testicular function in a number of genital conditions, reliable reference ranges are still lacking. The present study sought to establish the reference range for serum inhibin B by applying the updated Gen II assay.

This prospective study included 818 men referred for semen analysis: 377 were normozoospermic (reference group) and 441 presented at least one abnormal semen parameter (case group).

Semen parameters were interpreted according to the 2010 World Health Organization manual and David's modified classification for normal morphology. The inhibin B concentration was determined with the current ELISA.

In the reference group, the 2.5th percentile for inhibin B was 92 pg/ml and the 97.5th percentile for FSH was 7.8 IU/l. In the overall population, an inhibin B level <92 pg/ml was associated with increased odds ratio (OR; 95% CI) for oligozoospermia (16.93 (9.82-29.18), P<0.0001), asthenozoospermia (4.87 (2.88-8.10), P<0.0001), and teratozoospermia (2.20 (1.31-3.68), P=0.0026). The combination of a FSH >7.8 IU/l and an inhibin B <92 pg/ml was associated with greater OR for oligozoospermia (98.74 (23.99-406.35), P<0.0001) than for each hormone considered separately.

A new reference range for serum inhibin B was established by the use of updated immunoassay. The correlations between hormone levels and semen parameters highlighted the importance of establishing these values with respect to the spermogram. When combined with FSH assay, the inhibin B range may be of value in the evaluation of spermatogenesis in a number of male genital conditions.