Low Testosterone Explained: How Do You Know When Levels Are Too Low?

Although it’s normal for testosterone levels to drop as men age, low testosterone can affect a man’s health. In many ways, testosterone is the stuff that makes men men. The rush of new testosterone in puberty builds muscle and bone, deepens the voice, and revs up the sex drive. Throughout a man’s life, testosterone maintains his male characteristics.

Testosterone levels decline steadily after age 40. The decline is relatively small, at an average rate of about 1% to 2% percent per year. By middle age and older, virtually all men experience some decline in testosterone -- but only a small percentage of aging men have levels far below those considered normal for their age.

Is this low testosterone part of normal aging -- or a medical problem that needs treatment?

“If a man doesn’t have symptoms, you shouldn’t even test [for low testosterone],” says Karen Herbst, MD, PhD, an endocrinologist with the University of California at San Diego. “There’s no proof that treating low testosterone in the absence of symptoms has any benefits. But in men with symptoms of [low testosterone], many of them will get a benefit from treatment.”

What is Low Testosterone?

Low testosterone is defined as less than 300 nanograms per deciliter of blood. The symptoms of low testosterone include low sex drive, erectile dysfunction, mood problems, fatigue, and sleep disturbances. Of all men with below-normal testosterone levels, about one-half to two-thirds report symptoms.

Unlike a woman’s menopause, when estrogen levels plummet over months to very low levels, men’s “andropause” is a gradual decline of testosterone levels over years. The effects of low testosterone can be insidious, even go unnoticed.

Some men with low testosterone levels have symptoms without recognizing them, Herbst says. “They may still have a sex drive, but not realize how much it’s declined,” she says.

Men with symptoms of low testosterone can have significant impairment in quality of life. Current medical thinking is “these men should be treated with testosterone replacement,” Herbst says.

Low testosterone can be replaced by using a daily skin gel, patches worn on the skin, orally disintegrating tablets, or injections. The general recommendations are to raise the blood testosterone level only into the normal range.