Jim, a 70 year old man, comes in with significant symptoms of low testosterone including low libido, decreased energy and decreased concentration. He reports having his testosterone levels checked with is internist. He was told they were around 700ng/ml which is normal.
After a thorough history and physical, his hormone panel was repeated.
His total testosterone levels were 700ng/ml. However, his sex hormone binding globulin was 80nmol/L. Thus, his free androgen index was low. Treatment with testosterone replacement was started and his symptoms improved.
Total testosterone provides a look at the total amount of testosterone circulating in the bloodstream. However, 98% of testosterone is bound by proteins, only 2% is free in the bloodstream. In order for cells to utilize testosterone, it must be free or not attached to proteins. About 40% of testosterone is bound to SHBG and 55% to albumin or other proteins.
The problem with SHBG is once testosterone is bound to it, it is irreversible. Testosterone bound to albumin and other proteins can be freed and then utilized.
Thus, if your SHBG levels are high, there is less testosterone available for use.
In Jim’s case, his internist only looked at the total testosterone level and not what was available for his cells to use. We aimed for Jim to get to 1100ng/ml with his total testosterone. As his testosterone levels increased, more was available for use and his symptoms resolved.
Some conditions that lead to elevated SHBG levels include aging, chronic liver disease, hyperthyroidism and certain medications.
It is important to have a complete hormone panel done in order to identify all possible causes.