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The Importance of Testosterone Levels for Erection
“Current Concepts in the Evaluation and Management of Erectile Dysfunction”
Posted 11/26/2008 on
http://www.medscape.com
Pamela Ellsworth, MD, FACS; Eileen M.
Kirshenbaum, M.Ed, BSN, RN, CURN
Author Information
Testosterone secretion follows a circadian
pattern, with peak testosterone levels in the early morning and a nadir in
the late afternoon
(Cooke, McIntosh, & McIntosh, 1993). This circadian
pattern of testosterone secretion is lost in older men (Feldman et al.,
2002).
Testosterone exists in both an unbound and bound state. The bioavailable form of testosterone is the unbound testosterone and that which
is
bound to albumin. The inactive form of testosterone is that which is
bound to sex hormone-binding globulin (SHBG). Beyond 40 years of
age, the
total serum testosterone level decreases at an average rate of 0.8% per
year. In addition, the level of inactive testosterone, that
bound to SHBG,
increases with age at a rate of 1.5%.
The diagnosis of hypogona dism is by hormonal evaluation. It is rarely
identified by history and physical examination. Al though testosterone
positively affects libido, decreased libido may be related to other causes,
such as depression and lack of interest due to underlying ED.
Similarly, the
presence of normal secondary sex characteristics on physical examination
does not rule out a low testosterone level. In most
men, a morning total
testosterone level is all that is necessary. In older and obese males,
increased SHBG levels may aberrantly raise total
serum testosterone levels;
therefore, measurement of bioavailable testosterone, ideally via equilibrium
dialysis assay, is more accurate.
Although there are no clear-cut
testosterone levels that define hyoponadism, it is believed that levels less
than 250ng/dL are low, levels greater than 350 ng/dL are normal, and levels
between 250 ng/dL and 350 ng/dL are indeterminate. If the testosterone level
is low, then it is
appropriate to check LH, FSH, and serum prolactin levels.
Medications that may affect gonadal function include thiazide diuretics,
long-
acting oral opiates, antiepileptics, corticosteroids, and atypical
antipsychotic (such as risperidone and olanzapine) (Lunenfeld, 2003). If the
prolactin level is elevated, then further evaluation with an MRI is
indicated to rule out a pituitary adenoma.
What Level of Serum
Testosterone Level Warrants Treatment?
Current consensus
recommendations suggest limiting use of TRT to men with a serum testosterone
level of less than 200 ng/dL and
symptoms of hypogonadism, although evidence
supporting this recommendation is lacking (The Practice Committee of the
American
Society for Reproductive Medicine, 2004). Studies have demonstrated
that in individuals with low normal testosterone levels who have
failed oral
PDE-5 inhibitor therapy, an improvement in response to PDE-5 inhibitors with
testosterone supplementation exists (Shabsigh et
al., 2004). The use of TRT
for other factors, such as bone density and body fat mass, remains
controversial.
What Types of TRT Are
Available?
The ideal testosterone
preparation is that which allows for normalization of serum testosterone
levels, mimics the normal circadian pattern of
testosterone production,
produces normal levels of testosterone metabolites, and minimizes side
effects. Therapies currently used in the
United States include injectable,
topical, and transbuccal testosterone. Oral testosterone therapy is not used
in the United States due to the
inability to achieve adequate systemic
levels and the higher risk of adverse effects.
Table 4 lists the available formulations of testosterone.
What Are the Potential
Adverse Effects of TRT?
Side effects relative to the
individual preparation are listed in
Table 4 . TRT may increase prostate size and cause lower urinary tract
symptoms. In males on testosterone supplementation, the PSA may increase by
0.3ng/ml/year, whereas older men may experience up to a
0.43 ng/ml/yr change
in PSA when on TRT (Bhasin & Buckwalter, 2001). A baseline PSA should be
obtained before starting TRT and a
repeat PSA obtained 6 to 12 weeks after
starting therapy and semi-annually thereafter. Poly cythemia and sleep apnea
are more commonly
associated with the parenteral testosterone, and a
baseline hematocrit is recommended in individuals starting TRT and
periodically
thereafter.
The impact of TRT on
cardiovascular morbidity remains poorly defined. Physiologic doses of
testosterone have either no effect or
potentially beneficial effects on the
cardiovascular system. Caution should be used in men with congestive heart
failure, since testosterone
therapy may lead to an increase in hematocrit
levels (Kostis et al., 2005; Swerdloff & Wang, 2003). From a cardiovascular
standpoint,
higher-serum testosterone levels may be cardioprotective, and
changes in lipid profile are less relevant when the testosterone level is
restored to physiologic levels (Liu et al., 2003).
Changes in anticoagulant
activity may be seen with androgen use, and thus, individuals on
anticoagulants should have regular laboratory
testing. Concurrent use of oxyphenbutazone and androgens may lead to increased levels of
oxyphenbutazone. In diabetic patients, the
metabolic effects of androgens
may lower the blood glucose and insulin requirements. Concurrent admi ni
stration of testosterone with
adrenocorticotrophic hormone (ACTH) may
enhance edema formation, and the combination should be used with caution,
especially in
patients with cardiovascular or hepatic disease. |
