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By ManUnlocked Editorial | April 2026 | Medically Reviewed by Dr. Fatimah Khan, MBBS | Medical Disclaimer Applies
Your doctor orders a testosterone test. The result comes back: 480 ng/dL. The lab’s reference range says 264 to 916 ng/dL. Your doctor says you’re fine. Case closed.
Except you’re still tired. Still losing muscle. Still wondering why your libido packed up and left sometime around your 38th birthday.
Here’s what probably happened: your doctor tested total testosterone and nothing else. And total testosterone, by itself, is one of the most misleading numbers in men’s health.
What does total testosterone actually measure?
Direct answer: total testosterone measures all testosterone in your blood, including the portion that is tightly bound and not readily available for tissues to use.
Most men hear “testosterone” and assume the number on the lab sheet reflects what their body can actually use. It doesn’t.
About 98% of testosterone is bound to proteins. Roughly 60 to 70% is bound tightly to sex hormone-binding globulin, or SHBG. Another 25 to 35% is bound loosely to albumin. What’s left, usually about 1 to 3%, is free testosterone.
Think of it like your gross paycheck versus your take-home pay. Total testosterone is the gross number. Free testosterone is what actually reaches your wallet.
Why does SHBG change everything?
Direct answer: SHBG can make a normal total testosterone result functionally misleading by locking away a larger share of the hormone.
When SHBG goes up, it binds more testosterone and leaves less available to tissues.
Here’s what tends to raise SHBG:
- aging
- hyperthyroidism
- liver disease
- certain medications
- aggressive dieting or low caloric intake
- higher estrogen exposure
And what often lowers it:
- obesity or insulin resistance
- hypothyroidism
- glucocorticoid use
- nephrotic syndrome
- high-dose androgen use
This is why two men with the same total testosterone can feel completely different. One man with total T of 500 and SHBG of 20 may have healthy free testosterone. Another with total T of 500 and SHBG of 65 may have clinically low free testosterone despite a “normal” total number.
A classic study by Vermeulen et al. (1999) in JCEM showed that calculated free testosterone correlates more closely with symptoms of androgen deficiency than total testosterone alone.
How is free testosterone calculated?
Direct answer: free testosterone is usually calculated from total testosterone, SHBG, and albumin using the Vermeulen equation.
Free testosterone can be measured directly by equilibrium dialysis, but that method is expensive and not widely available. Most real-world clinicians rely on calculated free testosterone.
The Vermeulen equation models how testosterone binds to SHBG and albumin, then estimates the unbound fraction. When the input data are good, the calculated result tracks closely with direct measurement.
We built a free testosterone calculator based on this equation so you can estimate your free T from standard lab values.
Is the Free Androgen Index the same thing?
Direct answer: no, the Free Androgen Index is a rough shortcut and is not the same as calculated free testosterone.
Some labs report FAI instead of free testosterone. FAI is simply total testosterone divided by SHBG, multiplied by 100.
That shortcut performs poorly in men when SHBG is unusually low or high. If your lab only gives you FAI, ask for calculated free testosterone or use your raw values in our calculator.
What do the numbers actually mean?
Direct answer: total testosterone and free testosterone need to be interpreted together, not separately.
As a rough clinical guide:
Calculated free testosterone
- below about 6.5 ng/dL: usually considered low if symptoms are present
- 6.5 to 9.9 ng/dL: low-normal, where many symptomatic men still fall
- 10 to 20 ng/dL: healthy range for many adult men
Total testosterone
- below 300 ng/dL: below the usual diagnostic threshold for hypogonadism
- 300 to 450 ng/dL: low-normal or borderline
- 450 to 700 ng/dL: mid-range
- above 700 ng/dL: upper range
The key insight is that total T and free T do not always agree. A man with total T of 400 and low SHBG can have more usable testosterone than a man with total T of 600 and very high SHBG.
What if your doctor only tested total testosterone?
Direct answer: that is incomplete, especially if you still have symptoms.
This happens constantly. A lot of primary care evaluations stop at total testosterone, which means men with normal total T but low free T get told nothing is wrong.
If this happened to you, ask for:
- Total testosterone
- SHBG
- Albumin
- Calculated free testosterone
- LH and FSH
These are not exotic tests. They are standard lab components that should be part of a serious hormone workup.
What is bioavailable testosterone?
Direct answer: bioavailable testosterone includes free testosterone plus the albumin-bound fraction.
The idea is that albumin-bound testosterone dissociates easily enough to be usable by tissues.
Some clinicians like bioavailable testosterone as a middle-ground marker. In practice, calculated free testosterone is more widely used and usually easier to compare against clinical references.
What should you do with your results?
Direct answer: use total testosterone, free testosterone, SHBG, and symptoms together to decide what needs attention.
Here’s the practical framework:
Total T normal, Free T normal
Look elsewhere first. Sleep, thyroid, iron, stress, depression, and sleep apnea are bigger suspects.
Total T normal, Free T low
High SHBG may be making the total number look reassuring when it isn’t. This is the scenario many doctors miss.
Total T low, Free T low
That fits classic hypogonadism. Confirm with a second morning draw and discuss treatment with a specialist.
Total T low, Free T normal
This can happen with very low SHBG, often in obesity or insulin resistance. The total number may look worse than the biological reality.
What about genetically high SHBG?
Direct answer: some men are naturally prone to higher SHBG, and lifestyle changes may not lower it enough to solve symptoms.
This is the part almost nobody talks about. SHBG is partly genetic. Some men simply bind more testosterone than others because of how they’re wired.
That means “optimize your lifestyle” is good advice, but not always sufficient advice. If SHBG is genetically high, free testosterone can stay low even when total testosterone looks respectable.
Bottom line
Direct answer: total testosterone alone is not enough to interpret a hormone panel properly.
If your doctor only checked total T and told you you’re fine, that was not a complete evaluation.
Get total testosterone and SHBG tested. Calculate free testosterone. Bring both numbers to your next appointment. A doctor who understands the difference will take the conversation more seriously, and you’ll have a better shot at getting the right answer.
FAQ
Is free testosterone more important than total testosterone?
Neither should be used in isolation. Total testosterone shows overall circulating hormone, while free testosterone shows how much is actually available.
Can I lower SHBG naturally?
Sometimes modestly. Losing excess fat, reducing alcohol, and improving insulin sensitivity can help in some cases. But very high SHBG can also be partly genetic.
Why don’t all doctors test free testosterone?
Usually habit, cost concerns, or overreliance on total testosterone-only screening.
Is the Free Androgen Index the same as free testosterone?
No. FAI is a rough ratio and can mislead, especially in men with unusual SHBG levels.
The information on ManUnlocked.com is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any treatment, including testosterone replacement therapy. Individual results may vary.