Free Testosterone Is the Number That Actually Matters — And Most Labs Don't Even Test It

You get your testosterone results back: total T is 580 ng/dL. Your doctor says it's normal. But you feel terrible — fatigued, foggy, no libido. How is this possible?

The answer is likely hiding in a number that wasn't tested: your free testosterone. And understanding the difference between total and free testosterone is one of the most important concepts in men's hormonal health.

Total T vs. Free T: The Critical Distinction

Total testosterone measures everything — the testosterone bound to sex hormone-binding globulin (SHBG), the testosterone bound to albumin, and the small fraction that circulates freely. Roughly 98% of your testosterone is bound and biologically inactive. Only 2-3% is "free" — unbound and available to enter cells and exert its effects.

A man with total T of 580 but very high SHBG might have a free T that's equivalent to a man with total T of 300 and normal SHBG. The man at 580 looks fine on paper but functionally has low testosterone. His cells are seeing very little usable hormone.

What Drives SHBG Up (and Free T Down)

SHBG increases with age, hyperthyroidism, liver disease, estrogen (including from excess body fat), and certain medications. It decreases with obesity, hypothyroidism, high insulin levels, and anabolic steroid use. This is why context matters enormously — a total T level without SHBG and free T is an incomplete picture.

One common pattern: a man in his 40s or 50s with rising SHBG from age-related hormonal shifts. His total T holds steady at 500-600, but his free T drops progressively. He develops classic low-T symptoms — fatigue, reduced libido, brain fog — while his "normal" total T reassures his doctor that nothing is wrong.

How to Get Properly Tested

Request: total testosterone, free testosterone (calculated or by equilibrium dialysis — not the analog/direct method, which is unreliable), SHBG, and albumin. This panel gives you the complete picture. A morning blood draw (before 10am) is essential for accurate results.

If your doctor only runs total T and declares you normal, you don't have enough information to make a clinical decision. Push for the full panel, or seek a provider who orders it routinely.