I’ve been interested in the role of testosterone in physical performance, depression and aging for many years. While at the University of Iowa, I was involved in research to detect testosterone doping, the psychological effects of testosterone and the potential for testosterone to alleviate depression in older men.

One of the difficult questions facing clinicians is when is testosterone too low in older men.

One problem with answering this question is the physiological age-related testosterone decline. The “normal” range for testosterone is very different for 20 year old men compared to 80 year old men. So a simple blood test is not sufficient to answer the question of whether testosterone is too low.

But blood tests are best evaluated in the context of symptoms related to the tested parameter. This important relationship is highlighted in a recent New England Journal of Medicine study.

Frederick Wu from the University of Manchester in England and colleagues conducted a study to define when testosterone is too low. The medical terminology for this problem is hypogonadism.

Over 3000 men between 40 and 79 years of age completed assessments of general, sexual, physical and psychological health. Levels of testosterone were measure in blood samples collected in the morning.

Nine symptoms were endorsed by men with low testosterone: three psychological (loss of energy, downheartedness, fatigue), three physical (inability to engage in vigorous activity, inability to walk more than 1 kilometer, inability to bend, kneel or stoop) and three sexual symptom (infrequent thoughts about sex, erectile function problems, infrequent morning erections). In multivariate analysis the sexual symptoms proved to me the key distinguishing variables.

This study provides an answer to when is testosterone too low. And the answer is:

* When three sexual symptoms are present: infrequent thoughts about sex, erectile function problems, infrequent morning erections
* And total serum testosterone level is less than 3.2 ng/ml
* And free testosterone level is less than 65 pg/ml

Using these criteria produced a prevalence rate of late-onset hypogonadism ranging from 0.1% of men between 40 to 49 years up to a rate of 5.1% of men between the ages of 70 and 79.

So we now have an answer for a common clinical question. Since testosterone replacement is readily available more men will likely be pleased they asked the question “Is my testosterone too low?”

Testosterone replacement is not risk free, and may be related to risk for developing prostate cancer. Replacement should only be considered in consultation with a physician experienced in understanding the risk-benefit of such therapy.

William Yates is a family physician who blogs at Brain Posts.

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