Testosterone tips

[JanSz]

http://www.questdiagnostics.com/hcp/...newsletter.pdf
TESTOSTERONE TIPS
The American Association of Clinical
Endocrinologists has recently published
Medical Guidelines for Clinical Practice
for the Evaluation and Treatment of
Hypogonadism in Adult Male Patients—
2002 Update. Specific recommendations
are made for determining the most
effective methods for diagnosing and
treating hypogonadism in adult male
patients.
Hypogonadism is defined as “inadequate
gonadal function, as manifested
by deficiencies in gametogenesis
and/or the secretion of gonadal
hormones.” Initial laboratory testing
is often ordered by non-endocrinologists
and usually consists of measuring total
testosterone levels. An understanding
of the physiology of testosterone is
important in order to properly interpret
results of testosterone levels.
Testosterone levels may vary from
hour to hour, and periodic declines
below the normal range may occur in
normal men. A diurnal rhythm is
also present, with the highest levels of
circulating testosterone occurring
during the early morning hours.
Collection of samples for testosterone
levels should be done in the morning,
and studies should be repeated in
patients with subnormal levels,
especially those with no definite signs
or symptoms of hypogonadism.
Testosterone circulates principally
bound to sex hormone-binding globulin
(SHBG) and albumin. Testosterone
is tightly bound to SHBG and is not
biologically available. The portion bound
to albumin is weakly bound and can
easily dissociate to become free biologically
active testosterone. In young
adult men, only about 2% of testosterone
is in the free form, 30% is bound
tightly to SHBG and 68% is weakly
bound to albumin.
Although a total testosterone level
is the appropriate initial test in evaluating
possible male hypogonadism, the level
may be within the reference range in
men with primary testicular disorders.
Low production of testosterone and
increased estradiol stimulate hepatic
production of SHBG. The resulting
■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■
increased level of SHBG results in
higher circulating levels of total
testosterone than would otherwise be
present, along with low circulating
levels of free testosterone. Increased
SHBG may also be associated with
hyperthyroidism, liver disease, severe
androgen deficiency, or estrogen excess.
As men age, SHBG levels usually
increase about 1% per year. Male
patients with hypogonadism frequently
have high SHBG levels because of low
serum testosterone and enhanced
production of estradiol from increased
intratesticular aromatization.
If the clinical findings indicate or
suggest hypogonadism and total
testosterone levels are normal or
borderline low, the level of SHBG or
free testosterone by equilibrium
dialysis should be determined. In
borderline cases, measuring SHBG
can enhance the evaluation of total
testosterone levels. A low testosterone
level may also be misleading in
certain circumstances. Slightly low
levels of testosterone may occur in
men with low SHBG and normal
circulating levels of free testosterone.
Low levels of SHBG may be associated
with hypothyroidism, obesity, or
acromegaly. Determination of SHBG
levels or free testosterone by
equilibrium dialysis may be helpful
for clarifying the underlying disorder,
especially when the clinical findings
are not suggestive of hypogonadism.
The diagnosis and management of
hypogonadism is complex, and the
reader is referred to the cited reference
for an in-depth discussion of the topic.
(Endocr Pract 2002; 8(6): 439-456)