Sex Matters®: Louanne Cole Weston, PhD

Q . "I'm getting older and starting to have less interest in sex. Could it be time to add testosterone?"

The opinions expressed herein are the author's alone and have not been influenced by WebMD.

If you're a man nearly or over 50 and you find your sexual drive waning, you might indeed be a good candidate for testosterone supplementation. Before you go and get your testosterone levels tested, be sure you know the facts:

Laboratories vary in how they perform testosterone tests. To be sure of the result, have all your testosterone tests done at the same location at roughly the same time of day. (Hormones fluctuate throughout the day, so testing at about the same time is best.) Testosterone levels are most often measured with blood tests, but some centers utilize saliva tests as well.

According to Henry Ritter, MD, a urologist from Atherton, Calif., the most useful number to know is the "free testosterone" (or bioavailable testosterone). The "total testosterone" reflects free and bound testosterone. Bound testosterone is not available to boost libido because it is linked to proteins, such as albumin and sex hormone binding globulin, according to John E. Gould, MD, PhD, associate clinical professor of urology at the University of California at Davis. Gould also recommends getting the free testosterone number.

Different labs measure free testosterone differently. But ranges they consider "normal" generally fall between 260 nanograms/deciliter to 1,000 ng/dL (or 2.6 nanograms/milliliter to 10 ng/mL). Since physicians and laboratories have only recently begun to recognize the importance of testing free testosterone, you may have to lobby to get the test. If you are unable to get that reading and are forced to stick with total testosterone, learn the range of normal for your lab. Normal ranges for men usually are between 250 ng/dL to 1,200 ng/dL of blood (2.5 ng/mL to 12 ng/mL).

Keep in mind that these ranges are created by testing many men without much attention to their relative level of sexual function. Men whose testosterone level is in the lowest 20% of the normal ranges above may not feel much sex drive at all. In my clinical experience as a sex therapist, men with total testosterone readings in the low 400s tend not to have much sexual drive even if they are in fulfilling relationships. Ritter says that even some men in the 600s do not feel that much drive when other things are equal, and he prefers to see numbers in the 700s. Throwing things into further confusion, says Gould, is the fact that sometimes free testosterone will be low when the total testosterone is high and vice versa.

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