"Testosterone
within the circulation is principally bound to proteins, the most important of
which is sex hormone binding globulin (SHBG). Only about 2 percent of
testosterone is unbound (bio-available) and therefore free to enter cells in
order to effect its biological actions by binding to androgen
receptors...."
"Hypotestosteronaemia
levels [that is, low levels] quoted in papers
vary between around
300 ng/dl (10.4 nmol/L) and 400 ng/dl (13.9
nmol/L)."
"Bioavailable
testosterone refers to the 'free' portion of the hormone unbound to carrier
proteins which is able to act directly upon target tissues."
"It is well known
that androgen levels decline in men with age.
Furthermore, as a
result of the increase in binding capacity for
testosterone in serum,
there is an early and more dramatic decline in
free testosterone, the
physiologically functioning component of serum
testosterone, than in
the total testosterone concentration...."
"The ideal
therapy should consist of creating physiologic testosterone concentrations (400
to 700 ng/dL in blood taken in the morning) and restoring circadian
variations."
"Of great
interest is a recent finding that men with coronary artery
disease have
significantly lower levels of plasma testosterone than
controls and that
intracoronarv testosterone infusion in men with
coronary artery
disease increases coronary blood flow. Such findings
suggest that age
related declines in testosterone in men may be
associated with heart
disease ...."
Free Androgen Index (FAI): reference range is
1.6 to 2.9
"The FAI is the
ratio of total testosterone to SHBG. It provides a
simple assessment of
physiologically active testosterone.
FAI = 100 x TT (in
nmol/L) / SHBG (in nmol/L)"
Normal SHBG levels
vary widely: range at 13 to 71
nmol/L
Free Testosterone
(Bioavailable Testosterone):
Adult Male Reference
Interval
Free Testosterone: 47.0-244.0 pg/mL
% Free Testosterone:
1.6 - 2.9%
Testosterone
Age
20 - 39 years: 400 -
1080 ng/dL
40 - 59 years:
350 - 890 ng/dL
60 years and over:
350 - 720 ng/dL
Sex Hormone Binding
Globulin [SHBG]:
Age
13 - 15 years
13 -
63 nmol/L
16 - 18 years
11 -
54 nmol/L
19 - 150 years
13 -
71 nmol/L
LABORATORY SERVICES
HANDBOOK
Male Hormones
