What is the Origin of Free Testosterone Thresholds?

The concept arose from the understanding that total testosterone measurements often inaccurately reflect true androgenic activity due to variations in SHBG concentration. Endocrinologists developed the free testosterone assay to provide a more accurate measure of bioavailable hormone. Thresholds are defined by large-scale clinical data correlating specific concentrations with health outcomes and symptom resolution.

What is the Mechanism of Free Testosterone Thresholds?

Only free testosterone can diffuse across cell membranes and bind to intracellular androgen receptors to exert its genomic and non-genomic effects. SHBG acts as a physiological buffer, regulating the free fraction. When SHBG levels fluctuate due to metabolic or hormonal changes, monitoring the free testosterone threshold becomes critical for accurate assessment of androgen status and clinical management.

Free Testosterone Thresholds

Meaning

Free testosterone thresholds represent the clinically significant minimum and maximum circulating concentrations of biologically active, unbound testosterone necessary to maintain optimal physiological function. Free testosterone is the fraction of the hormone not bound to sex hormone-binding globulin (SHBG) or albumin, making it readily available to target tissues. Maintaining levels above the lower threshold is essential for robust muscle mass, libido, and energy.