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There has been a recent flurry of marketing for products to provide men with supplementary testosterone. More specifically, these prescription products are marketed as testosterone replacement therapies. As a replacement therapy, the implication is that some men need to have testosterone replaced. However, it is not entirely clear if healthy men need testosterone replacement or if testosterone replacement therapy is actually beneficial for most men.
The concept of testosterone deficiency is somewhat murky. In women, the concept of oestrogen deficiency is rather straightforward. Once women progress through menopause, there is a profound drop in oestrogen levels. While it is true that testosterone levels decrease as men age, the decline is not nearly as abrupt and profound as oestrogen deficiency in women. It is unclear what “normal” levels should be for men at what point testosterone replacement therapy is needed. Moreover, a man's testosterone level changes throughout the day, which makes defining “normal” and “below normal” even more challenging.
Between the ages of 40 and 79, total testosterone can be expected to decline 0.4% each year and free testosterone (i.e. testosterone unbound to protein in the blood) decreases by 1.3% each year. a substantial number of men, however, will have lower than normal levels of testosterone in the blood as they age. For example, over 50% of men have abnormally low testosterone by the time they reach the age of 80. Since more than half of men have “abnormally low testosterone”, it is quite difficult to determine “normal” values.
Roughly 2% of men have testosterone deficiency syndrome which is an abnormally low testosterone level and at least three sexual symptoms. These men are likely to also experience abnormally low hemoglobin, decreased bone mineral density, decreased muscle mass, and reduce physical performance. In addition, men with very low testosterone levels also have increased rates of insulin resistance (a condition that is related to type 2 diabetes).
As with any blood measurement, normal and abnormal ranges vary by laboratory. Thus, normal and abnormal levels defined by a particular laboratory should be used. In one scientific study, normal testosterone levels were defined as being greater than 325ng/dL or 11.3nmol/L. Total testosterone levels below 200ng/dL or 6.9nmol/L are usually considered substantially low and usually indicate the need for additional investigation. Free testosterone—a measure that may more accurately reflect true testosterone levels in obese men—should be more than 35 pg/mL in men less than 70 years old and more than 30 pg/mL in older men. In some laboratories, however, the normal range for free testosterone may be 5–9 pg/ml (0.17–0.31 nmol/L).
Since testosterone levels change throughout the day, especially in younger men, diagnostic blood draws should be done between 8 and 10 AM every time. If the morning blood draw reveals normal free testosterone, the man should not receive testosterone replacement therapy unless there is some testosterone related deficiency in sperm production or other endocrine disease.
If the first free testosterone measurement is abnormally low, the test should be repeated on a different day along with two other hormones: luteinizing hormone and follicle-stimulating hormone.
Again, a normal free testosterone level on the second test should be considered evidence of normal testosterone. If free testosterone is low, but luteinizing hormone and follicle-stimulating hormone are normal, the diagnosis is secondary hypogonadism. In cases of secondary hypogonadism, additional testing may be performed including:
If free testosterone is low and luteinizing hormone and follicle-stimulating hormone are high, the diagnosis is primary hypogonadism and a karyotype should be performed. A karyotype is a test in which the number of chromosomes is counted under microscope. Primary hypogonadism may indicate a genetic disorder and is usually diagnosed early in life rather than at the time men become concerned with testosterone deficiency.
Low testosterone levels may be associated with a number of undesirable symptoms. While the causal link has yet to be shown definitively through clinical trials, evidence suggests that low testosterone causes:
Testosterone supplementation has been shown to modestly help increase libido and sexual potency, mood, muscle mass and fat mass, and bone density.
Older men are particularly prone to testosterone-related diseases. Testosterone replacement therapy theoretically increases the risk of prostate cancer, benign prostatic hyperplasia, sleep apnea, and an increase red blood cell count. At the current time, it is unclear whether testosterone replacement therapy poses a significant risk or if the benefits outweigh potential risk.
Since it is difficult to determine what is normal and abnormal for testosterone levels by age, it is also difficult to determine what an appropriate level of replacement should be. Since there are several negative effects of elevated testosterone in older men, is considered imprudent to attempt to restore testosterone to the levels of a young man.
Therefore, treatment goals for serum total testosterone concentration should be between 300 and 400 ng/dL or 10.4 and 13.9 nmol/L. The goal of treatment is to raise testosterone levels and treat the effects of low testosterone without greatly increasing the risk of testosterone-related side effects.
Testosterone replacement drugs include oral preparations, long-acting injections, extra-long-acting injections and topical treatments. Oral testosterone preparations may be less effective at treating sexual symptoms of low testosterone and can cause several harmful effects on the liver including jaundice and liver cancer. Therefore, oral testosterone is rarely used for testosterone replacement therapy, if at all.
Long-acting injections and extra-long-acting injections can be effective in normalising testosterone levels and only need to be administered once a month or once every three months, respectively. The drugs are injected deep within a muscle, and testosterone slowly leaks into the bloodstream over time. While treatment is convenient because it only is required in frequently, more or less testosterone may leak out over time leading to fluctuations in blood testosterone.
Modern treatment for testosterone replacement therapy usually involves some sort of topical treatment. This may include transdermal patches or topical ointments. Androderm is a patch worn on the arm or abdomen that delivers between 2 to 4 mg of testosterone every day. Other testosterone patches are available in some countries. AndroGel, Axiron, Fortesta, and Testim are testosterone gels that deliver varying amounts of testosterone. While the percent of testosterone varies from 1 to 2% by drug, the amount of testosterone delivered varies much more than that. Because of the potency of testosterone gels, it is important to follow prescribed treatment recommendations precisely to achieve treatment benefit and avoid complications.
Other forms of testosterone that may be used to treat testosterone deficiency include a tablet that dissolves in the mouth (Striant SR), a testosterone pellet that is placed under the skin (Testopel), and a nasal testosterone gel (Natesto).