What is free testosterone?
Free testosterone is the small fraction of testosterone circulating unbound in the blood, which is biologically active and available to tissues, as opposed to testosterone bound to carrier proteins.
Most testosterone in the blood is bound to sex hormone-binding globulin (SHBG) or albumin, making it unavailable for cells to use. Free testosterone refers to the unbound testosterone molecules circulating freely in the bloodstream, typically accounting for less than 2 percent of total testosterone. Only free testosterone can enter cells and produce the androgenic effects people seek through treatment.
Many TRT clinics in Miami measure free testosterone separately from total testosterone because total levels alone do not reveal how much hormone is actually usable by the body. A patient may have adequate total testosterone but low free testosterone if SHBG levels are elevated. Conversely, free testosterone can be elevated even when total testosterone is normal, which matters for symptom assessment and dose adjustments.
Clinics typically measure free testosterone using one of two methods. Equilibrium dialysis is considered the most accurate laboratory technique but is expensive and rarely used outside research settings. Most providers use calculated free testosterone, derived from total testosterone, SHBG, and albumin measurements using established equations. While less precise than dialysis, calculated free testosterone provides practical, cost-effective results suitable for clinical decision-making and monitoring during treatment.