Your testosterone can look fine on paper and still not do what you expect. Often the answer sits in SHBG, a protein that binds testosterone and so determines how much is really available. Without knowing SHBG, you only read a testosterone result halfway.
This article explains what SHBG is, why the value fluctuates, and how it affects your free testosterone. You'll also see why two men with exactly the same total testosterone can still feel very different, and what SHBG has to do with that.
What is SHBG?
SHBG stands for sex hormone-binding globulin, a protein your liver makes. It binds sex hormones, mainly testosterone, and carries them through your blood. As long as testosterone is attached to SHBG, it isn't directly available to your cells.
You can see SHBG as a kind of taxi company for testosterone. If a lot of testosterone is in the taxi, less is out on the street for immediate use.
So SHBG is essential for reading your testosterone values well.
How does SHBG affect your testosterone?
The higher your SHBG, the more testosterone is bound and the less stays freely available. Two men with exactly the same total testosterone can therefore have very different free testosterone.
Researchers show that a calculation of free testosterone based on SHBG is often more informative than total testosterone alone (Vermeulen et al., J Clin Endocrinol Metab, 1999).
We work out the difference between total and free testosterone in free versus total testosterone.
What makes SHBG rise or fall?
SHBG isn't fixed. The value moves with your age, your weight, your thyroid and more. That makes it a dynamic factor in your hormone balance.
| SHBG moves | Factors that relate to it |
|---|---|
| Higher | Increasing age, an overactive thyroid, sometimes liver problems |
| Lower | Excess weight, insulin resistance, an underactive thyroid |
Because SHBG can change, your free testosterone can shift while your total testosterone stays the same. That explains why complaints and results sometimes seem not to match.
The NHG stresses that hormone values are always looked at in combination, not in isolation.
In practice that means you best read SHBG alongside your testosterone and your symptoms. A high or low SHBG is no goal in itself, but a piece of context that helps you understand your testosterone.
When is SHBG interesting to measure?
SHBG is mostly useful when your testosterone result and your symptoms don't line up. If a man feels tired or flat while his total testosterone looks normal, SHBG can solve part of the puzzle.
With excess weight or thyroid complaints, SHBG can also add context, because those relate to SHBG.
If you want testosterone, free testosterone and SHBG measured together, a men's hormone test brings them into view. The broader frame is in the pillar men's hormones.
Frequently asked questions about SHBG
Is a high SHBG bad? Not by definition. A higher SHBG means more testosterone is bound, which gives context, not a diagnosis.
Can I influence my SHBG? SHBG relates to factors like weight and thyroid, so lifestyle plays an indirect role. Big, fast changes aren't realistic.
Why is SHBG on my hormone result? Because it helps read your testosterone well. Without SHBG, free testosterone is harder to estimate.
What is a normal SHBG value? Reference values differ per lab and per age. Your result states the range that fits your measurement.
Is SHBG linked to my weight? Excess weight and insulin resistance relate to a lower SHBG, so weight plays an indirect role.
Does every hormone test measure SHBG? Not always, but a men's hormone test often includes SHBG because it helps read your testosterone.
What you can do with this
SHBG is the quiet regulator behind your testosterone. If you want an honest picture of your hormones, look at SHBG and testosterone together. A single SHBG value says little, a series over time more. Doubt a result or have complaints? Discuss it with your GP.
Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss symptoms and treatment decisions with your GP.
References
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999. PMID: 10523012.
- NHG. Dutch College of General Practitioners: hormonal diagnostics. Accessed 2026.
- RIVM. Public health and care: thyroid and metabolism. Accessed 2026.
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