Free Testosterone

Most testosterone in blood travels attached to proteins. A portion is tightly bound to sex hormone binding globulin, another portion is more loosely associated with albumin, and a small fraction is unbound. The term free testosterone refers specifically to that unbound fraction. Bioavailable testosterone is a related but different term that may include free and albumin-bound hormone.

Free testosterone can be measured directly with certain laboratory methods or estimated from total testosterone, SHBG, and sometimes albumin. Direct assays and calculations have different limitations, especially at low concentrations. Results should therefore be interpreted with the method, reference interval, collection time, and laboratory context visible rather than compared as if every test were identical.

A free testosterone value does not stand alone. Changes in SHBG can alter the relationship between total and free hormone, and SHBG itself can vary with age, thyroid status, liver conditions, medications, and other factors. Symptoms attributed to hormones are often non-specific. A qualified practitioner considers the full pattern, the person's history, and repeat testing when appropriate before drawing clinical conclusions.

Equilibrium dialysis is commonly regarded as a reference approach for separating the free fraction, while calculated estimates are more widely accessible. The distinction matters because a report may label both simply as free testosterone. The method printed on the report helps explain what the number represents and how cautiously two results can be compared.

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