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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.
Also known as: Free Testosterone, Free Testosterone (calc), Free Testosterone (Calculated), Free Testosterone Calculated, Testost Free, Testosteron.frei, Testosteron.serb, Testosterona.livre
High free testosterone amplifies androgenic symptoms. Low free testosterone causes hypogonadal symptoms even when total testosterone appears normal, particularly when SHBG is elevated.
Standard male range is 5-21 pg/mL. Functional target is 15-25 pg/mL for men. Free testosterone represents only 1-3% of total testosterone.