Understanding Total vs. Free Testosterone
Total testosterone measures all testosterone in your blood—both the testosterone that's bound to proteins and the small amount that's free, while free testosterone measures only the active portion that's not attached to proteins and can actually be used by your body's tissues.
What Total Testosterone Tells Us
Total testosterone represents the complete amount of testosterone circulating in your bloodstream 1. This includes:
- Testosterone tightly bound to SHBG (sex hormone-binding globulin) – approximately 60-70% of your total testosterone is locked onto this protein and cannot be used by your body 2
- Testosterone loosely bound to albumin – about 30-40% is attached to this protein but can be released when needed 2
- Free testosterone – only about 2% of your total testosterone floats freely in the blood 3, 2
The normal range for total testosterone in adult men is approximately 264-916 ng/dL, with an average around 500-600 ng/dL 1. However, this number alone doesn't tell the complete story of how much testosterone your body can actually use.
What Free Testosterone Tells Us
Free testosterone is the metabolically active fraction—the portion that can enter your cells and produce effects like maintaining sex drive, muscle mass, and energy 2. This is the testosterone that actually matters for your body's function 2.
Free testosterone typically ranges from about 0.245-0.785 nmol/L (approximately 7-23 ng/dL) in healthy men 3. Because it represents such a small percentage of total testosterone, small changes in the proteins that bind testosterone can dramatically affect how much free testosterone you have available, even when total testosterone looks normal 1.
Why Both Measurements Matter
In men with obesity, borderline testosterone levels, or certain medical conditions, total testosterone can appear normal or only slightly low while free testosterone is actually quite low 1. This happens because:
- Conditions like obesity, diabetes, and aging can increase SHBG levels, which binds more testosterone and leaves less free testosterone available for your tissues 1, 4
- Up to 8.4% of men with sexual symptoms have hypogonadism that would be missed if only total testosterone is measured 4
- Free testosterone correlates better with symptoms like low libido, erectile dysfunction, and fatigue than total testosterone does 4
When Free Testosterone Should Be Checked
Your doctor should measure free testosterone (by equilibrium dialysis or calculation) in addition to total testosterone when 1:
- Your total testosterone is near the lower limit of normal (approximately 230-350 ng/dL) 1
- You have obesity, as excess body fat increases SHBG and can mask true testosterone deficiency 1
- You have diabetes or metabolic syndrome 1
- Your symptoms suggest low testosterone but your total testosterone appears borderline normal 4
The Bottom Line
Think of total testosterone as the money in your bank account—some is locked in long-term investments (SHBG-bound), some is in a savings account you can access if needed (albumin-bound), and some is cash in your wallet (free testosterone). Only the cash in your wallet is immediately available to spend, just as only free testosterone is immediately available for your body to use 2. Measuring both gives your doctor the complete picture of your testosterone status and helps avoid missing a diagnosis when total testosterone alone looks deceptively normal 4.