Summarized & reviewed by The Peptide Dispatch Editorial Team · Last reviewed July 27, 2026
There is a specific and very common clinical situation that goes something like this. A man in his late forties reports low energy, flat mood, poor recovery from training, and a body composition that has been drifting the wrong way for two years. His physician orders a testosterone level. It comes back at 480 ng/dL. The reference range printed next to it runs roughly 264 to 916. The result is…
This dispatch covers Your Testosterone Result Is a Number About a Protein You Have Never Heard Of in the metabolic research category, authored by The Peptide Dispatch Editorial Team. Estimated reading time: 8 minutes. The Peptide Dispatch curates peer-reviewed peptide research for self-directed learners. All summaries are presented for Research Use Only and do not constitute medical advice.
There is a specific and very common clinical situation that goes something like this. A man in his late forties reports low energy, flat mood, poor recovery from training, and a body composition that has been drifting the wrong way for two years. His physician orders a testosterone level. It comes back at 480 ng/dL. The reference range printed next to it runs roughly 264 to 916. The result is inside the range, so the conversation ends there. The problem is that 480 ng/dL is not a measurement of how much testosterone is available to his tissues. It is a measurement of how much testosterone is present in his bloodstream, the overwhelming majority of which is chemically unavailable to do anything at all. Whether that 480 represents a comfortable androgen status or a functionally deficient one depends almost entirely on a liver protein called sex hormone binding globulin, or SHBG, which most panels do not measure. What total testosterone is actually counting Testosterone circulates in three states. A small fraction, typically 1 to 3 percent, floats free in plasma. A larger fraction is loosely bound to albumin, held weakly enough that it dissociates readily at the capillary and is generally considered available to tissue. The remainder, often 40 to 60 percent or more, is locked to SHBG with high binding affinity. The free hormone hypothesis, which underpins most of endocrine physiology, holds that only the unbound and weakly bound fractions can enter cells and act on the androgen receptor. The SHBG-bound portion is essentially in storage. It is real testosterone, it shows up on the assay, and it is doing nothing for muscle, mood, libido, bone, or metabolic function while it stays bound. A total testosterone result adds all three pools together and reports one number. Two men can both return 480 ng/dL and have meaningfully different androgen exposure, because one has SHBG of 25 nmol/L and the other has SHBG of 70 nmol/L. The second man has far more of his testosterone…
Educational content — not medical advice. Effects described are drawn from cited research in study subjects.