How do testosterone levels change throughout the day: Highs and lows How Aging Affects Testosterone and Muscle Mass in Men Due to the challenges in testosterone methodology, there is considerable variability in testosterone reference ranges.13  The specific reference ranges used to diagnose testosterone deficiency are discussed in more depth later in this document. However, practicing clinicians who review testosterone lab results will commonly face the dilemma of whether to use the reference ranges published by their specific lab or the absolute measure itself. As an example, a total testosterone value of 250 ng/dL may be considered low based on the current guideline but be marked within the normal range by the laboratory. This situation commonly occurs as reference laboratories often define a normal value as ranging within the 5th (or 2.5th) and 95th (or 97.5th) percentiles of a sampled population. It stimulates the development of male characteristics and is essential for sperm production (spermatogenesis). Levels of testosterone are naturally much higher in men than women. When people enter menopause, their estrogen levels typically drop. This, in turn, makes their male hormones, also known as androgens, somewhat higher. After several intermediate steps, cholesterol is converted into androstenedione, the hormone made infamous by Mark McGwire as the unregulated “dietary supplement” andro. Whether androstenedione comes from the body or a bottle, it is rapidly converted into testosterone. TRT seems to be more effective in young men with very low testosterone levels. Some studies suggest that saliva tests can also provide an accurate measure of testosterone levels in the body. Finding the appropriate balance of testosterone is possible through discussions with your doctor, and it requires your willingness to have testosterone levels checked before the initiation of therapy and then checked routinely in the future. Finding a doctor who understands this is very important to optimizing your care. After you have been started on some form of treatment, you should have a follow-up visit to discuss how your symptoms are being controlled and to have follow up blood test to measure your testosterone levels, your blood count. This is important because a small percentage of patients may see a mild thickening of their blood or hematocrit. If you are over 50 or have a family history of prostate cancer, you should have a screening test for prostate cancer or PSA as well. If patients achieve target testosterone levels, but do not feel that they have sufficient improvement in their symptoms, clinicians should question whether testosterone deficiency is the etiology of their symptoms. Potential signs and symptoms include a lowered sex drive (libido), erectile dysfunction, loss of facial or body hair, loss of muscle mass, thinning bones, enlarged breasts, unexplained anemia, low sperm count and reduced energy. The most common “out of balance” testosterone levels are found to be on the low side of normal; this occurs because a male’s highest testosterone level usually peaks at about age 20, and then it decreases slowly with age. It has been suggested that a 1% decrease in