Serum inhibin-b in fertile men is strongly correlated with low but not high sperm counts: a coordinated study of 1,797 European and US men.
OBJECTIVE
To describe associations between serum inhibin-b and sperm counts, adjusted for effect of time of blood sampling, in larger cohorts than have been previously reported.


METHODS
Cross-sectional studies of spermatogenesis markers.


METHODS
Four European and four US centers.


METHODS
Fertile men (1,797) were included and examined from October 1996-February 2005.


METHODS
The study was observational and therefore without any intervention.


METHODS
Associations between inhibin-b and semen variables controlled for time of blood sampling and other covariates.


RESULTS
Inhibin-b decreased about 2.00% per hour from 8 am-12 pm and then about 3.25% per hour from 12 pm-4 pm. There was a strong positive association between inhibin-b levels less than 150 pg/mL and both sperm concentration and total sperm count (slopes of the regression lines were β=0.011 and β=0.013 for natural logarithm-transformed sperm concentration and total sperm count, respectively). For inhibin-b levels of 150-300 pg/mL the associations were not as steep (β=0.002), but still significant. For inhibin-b levels more than 300 pg/mL there was little association to the sperm counts. Neither sperm motility nor morphology was significantly related to inhibin-b level in any group.


CONCLUSIONS
Serum inhibin-b levels decrease nonlinearly during the daytime, and are positively correlated with sperm counts, but the predictive power is best when inhibin-b is low.
University Department of Growth and Reproduction, Rigshospitalet, Copenhagen, Denmark. Niels.Joergensen@rh.regionh.dk
Niels
N
Jørgensen
Fan
F
Liu
Anna-Maria
AM
Andersson
Matti
M
Vierula
D Stewart
DS
Irvine
Jacques
J
Auger
Charlene K
CK
Brazil
Erma Z
EZ
Drobnis
Tina K
TK
Jensen
Pierre
P
Jouannet
James W
JW
Overstreet
J Bruce
JB
Redmon
Amy
A
Sparks
Jorma
J
Toppari
Christina
C
Wang
Niels E
NE
Skakkebæk
Shanna H
SH
Swan
D000328:Adult; D015415:Biomarkers / Q000097:blood; D001800:Blood Specimen Collection; D002940:Circadian Rhythm / Q000502:physiology; D003430:Cross-Sectional Studies; D005060:Europe / Q000453:epidemiology; D005298:Fertility / Q000502:physiology; D006801:Humans; D007265:Inhibins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009845:Oligospermia / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D011237:Predictive Value of Tests; D013076:Sperm Count; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
D015415:Biomarkers; C422364:inhibin B; D007265:Inhibins