Total Testosterone Is Only Part of the Picture
Even if your total testosterone looks acceptable, it doesn’t tell you how much of that testosterone is actually available to your tissues. Testosterone circulates in the blood in three forms: tightly bound to sex hormone-binding globulin (SHBG), loosely bound to albumin, and free. Only the free and albumin-bound fractions are biologically active.
SHBG levels increase with age, with certain medications, and with thyroid dysfunction. A man with a total testosterone of 18 nmol/L but very high SHBG may have less bioavailable testosterone than a man with a total of 12 nmol/L and low SHBG. If your doctor only ordered total testosterone — which is the default in most GP panels — you have an incomplete picture.
A proper workup includes free testosterone, SHBG, LH, FSH, prolactin, estradiol, and a full metabolic panel. Without those, you’re making decisions with half the data.
