What Is a Free Testosterone Blood Test?

Free testosterone is the unbound, biologically active form — only 1–3% of total testosterone.

Why Test Free T?

• Total T can be misleading
• SHBG binds testosterone — high SHBG = low free T
• Symptoms may reflect free T, not total T

Factors Affecting SHBG

• High SHBG: aging, liver disease, hyperthyroidism, estrogen
• Low SHBG: obesity, insulin resistance, hypothyroidism

When to Test Free T

• Symptoms of low T but total T is borderline
• Conditions affecting SHBG
• Monitoring TRT effectiveness