About Testosterone, Free
Free testosterone is the biologically active fraction of testosterone that is not bound to carrier proteins (SHBG or albumin) and is directly available to tissues. Total testosterone can be misleadingly normal while free testosterone is low — particularly in individuals with high SHBG from aging, liver stress, or thyroid dysfunction. Symptoms of low testosterone (fatigue, low libido, muscle loss, brain fog) correlate more closely with free testosterone than total testosterone.