Inhibin B is an important
serum marker of spermatogenesis, whereas sensitivity and predicting power for the spermatogenic situation at several ages are under debate. We performed a retrospective analysis of data from 2448 men who attended our University-based
male infertility clinic to evaluate
inhibin B in relation to age and semen sample qualities in comparison with FSH. Moreover, the range of
inhibin B in 82 nonobstructive azoospermic patients was correlated with the sperm retrieval in testicular sperm extraction procedures.
Inhibin B correlated with FSH (Spearman rank correlation (R)=-0.50; P<0.00001).
Inhibin B and
inhibin B/FSH ratio (IFR) showed an inverse U-shaped dependence on age, whereas FSH showed a U-shaped dependence on age (optimum 20-40 years). However, in men with normal spermiograms
inhibin B concentrations did not differ between age groups. Their levels of
inhibin B amounted to 130.5, 54.5-247 ng/l (median, 10th-90th precentile), and of IFR to 38.3, 12.5-104.8 (median, 10th-90th percentile), which might be taken as the reference range. Using the 10th percentile of IFR, correct classification in normal or pathological semen groups was achieved in 99.1%. The percentage of
aniline blue-negative spermatozoa, i.e. mature spermatozoa with
protamines, did not correlate with FSH (P>0.05) but with
inhibin B (R=0.15, P<0.001). The probability of retrieving testicular spermatozoa decreased with declining
inhibin B: <20 ng/l sperm could never be found. Our results from a large group of men with a wide spectrum of semen qualities allow estimating reference values for
inhibin B and IFR.
Inhibin B and especially the IFR are more sensitive markers of
male infertility than FSH alone.