when comparing populations, AGD may provide a useful,
more reliable, and less variable metric than testis volume or
sperm production as the latter two may be influenced by
trauma, age, or medical treatment (i.e. testosterone
therapy).[
11
,
24
] However, newer reports does suggest some
plasticity to AGD in adult life thus questioning this theoretical
benefit.[
25
]
It is uncertain why AGD is correlated with certain semen
parameters (e.g. sperm concentration) but not others (e.g.
motility or volume). While concentration may reflect germ
cell number, motility may reflect germ cell number, and
volume may reflect seminal vesicle and prostate function;
rodent studies imply that all may be impacted.[
22
,
23
]How-
ever, in human, only changes in sperm numbers were
identified.
Certain limitations warrant mention. Working in a
referral center for male infertility, it was not always
possible to blind observers to the men's diagnoses,
which theoretically can have led to observer bias. How-
ever, the semen analysis was rarely known at the time
of AGD measurement. In addition, only men referred to
and evaluated in our clinic were eligible for enrollment;
therefore, it is possible that our patient population does
not represent all men. Indeed, a majority of men with
semen data were evaluated for infertility which may
impact the generalizability. However, as half of the
men were fathers both fertile and infertile men were
included. While psychological and physical discomfort
may be a concern regarding AGD measurement, <0.5 %
of men expressed any reservation regarding the
measurement.
Nevertheless, the current study is the first to examine
the benefit of an AGD measurement in a male infertility
evaluation. While providing some information about
sperm production, other routinely collected parameters,
such as testis size are more strongly correlated with
fertility. However, AGD does correlate with sperm
Table 4
Area of the curve (AUC) based on receiver operating charac-
teristic analyses for AGD and total testis volume when examining mea-
sures of male fertility
AUC
Characteristic
AGD
Total testis size
p
Fatherhood
0.63
0.71 0.02
Low Ejaculate Volume (<1.5 mL)
0.52
0.41 0.05
Oligospermia (<15 M/mL)
0.61
0.69 0.1
Asthenospermia (<40 %)
0.54
0.53 0.81
Low Total Sperm Count (<39 M)
0.66
0.74 0.08
Low Total Motile Sperm Count
(<9 M)
0.62
0.68 0.24
Table 5
Menstratifiedintoshort(<median AGD, 37.6 mm) versus long (
≥
median AGD) as well as small (<average testis size of 16 cm
3
) versus large testis (
≥
average testis size of 16 cm
3
). Mean values
of AGD, total testis volume, semen volume, sperm concentration, and sperm motility are listed. AUC (area under the curve) for each subgroup listed using AGD and testis volume as predictors and
fatherhood the outcome.
AUC
AGD
Testis
n
AGD (mm)
Total testis volume (mL)
Semen volume (mL)
Sperm concentration (M/mL)
Sperm motility (%)
Fathers n (%)
AGD
Testis
p
Short
Small
71
26.8
26.5
2.6
7.1
24.7
16 (22.5)
0.55
0.66
0.25
Short
Large
165
29.6
38.5
2.5
17.2
25.4
76 (46.1)
0.59
0.68
0.11
Long
Small
39
51.1
25.8
3.5
2.3
14.4
12 (30.8)
0.48
0.62
0.41
Long
Large
194
49.2
39.2
2.8
29.7
31.7
122 (62.9)
0.57
0.64
0.20
P
value represents comparison between AGD and testis volume to predict fatherhood