If you have ever left a doctor’s office holding a “normal” testosterone result while still feeling tired, foggy, or simply not yourself, you are not alone. It is a frustrating place to be, because the number on the page seems to close the conversation before your symptoms have had their say. Many men sit with exactly this gap between how they feel and what the lab reports, and rest assured there is often a sensible explanation behind it.
One of the most common explanations has a slightly clumsy name, sex hormone-binding globulin, usually shortened to SHBG. Understanding how it shapes your testosterone reading can change the way you read your own results, and the way you talk about them with the person treating you. In this blog post, we will discuss what SHBG is, how it affects the testosterone your body can actually use, and the questions worth bringing to your next appointment.
What Does Testosterone Actually Do in Your Body?
Before we get to SHBG, it helps to picture what testosterone is doing day to day. It is produced mainly in the testes, then it travels through your bloodstream to reach tissues all over the body, such as muscle, bone, brain, and the reproductive organs.
A standard blood test measures the testosterone circulating in your blood. However, that single figure hides an essential detail, because not all of that testosterone is equally available to your cells. Some of it is busy, and some of it is free to work.
What Is SHBG, and Where Does It Come From?
SHBG is a protein made largely by your liver, and its task is to bind to sex hormones in the bloodstream, including testosterone and estradiol. When testosterone is tightly bound to SHBG, it cannot easily slip into your cells to do its job. Think of it as testosterone that is present in your circulation yet essentially locked away.
A smaller share of testosterone is loosely attached to albumin, another blood protein, and that bond comes apart far more readily. The testosterone that is either completely free or only loosely held by albumin is what clinicians call “bioavailable” testosterone, meaning the portion that can genuinely act on your tissues.
So two men can share the same total testosterone number and still have very different amounts of usable hormone, depending on how much SHBG each one is carrying.
Total, Free, and Bioavailable: What the Measurements Mean
When your clinician orders a routine testosterone test, the result is usually total testosterone, the sum of everything in your blood whether it is bound or free. However, that total does not reveal how much is actually reaching your cells.
Free testosterone refers to the small fraction tied to no protein at all. In practice, this is often estimated rather than measured directly. Calculated free testosterone is worked out from your total testosterone, SHBG, and albumin using a mathematical formula.[1]
It is helpful to know that this calculated value is an estimate, not a direct reading. The formulas have recognised limitations, and results can shift from one laboratory to another.[1]
When Does SHBG Matter Clinically?
A man with a high SHBG level has more of his total testosterone bound up and out of reach, even when that total sits comfortably in the normal range. In some cases this can produce symptoms that look very much like low testosterone, despite a reassuring lab result. If this sounds familiar, our overview of low testosterone symptoms may help you make sense of what you are feeling.
This is exactly why clinical guidelines suggest looking at free or calculated free testosterone alongside the total when a clinician suspects SHBG may be off, such as in older men or in those with conditions known to alter SHBG.[2][3]
However, there is no single, universally agreed cutoff for what counts as a “low” free testosterone level. This is one of those areas where the full clinical picture, rather than one number, carries the weight.[1][3]
What Can Affect Your SHBG Levels?
Several things are linked to changes in SHBG, and knowing them helps explain why two results can look so different.
Age plays a clear role. In a cohort study of more than 1,700 community-dwelling men, SHBG rose with age, which is part of why older men can have less bioavailable testosterone even when their total testosterone has barely moved.[4]
Body weight matters too. In that same cohort, greater abdominal fat mass was associated with lower SHBG, which fits the wider pattern linking excess body fat to lower SHBG in men.[4]
Thyroid function pulls SHBG in opposite directions. An overactive thyroid (hyperthyroidism) tends to raise SHBG, while an underactive thyroid (hypothyroidism) tends to lower it.[5]
Because SHBG is made in the liver, conditions that affect liver function can also influence how much SHBG you produce.[6]
None of this is a list of diagnoses. These are simply the factors a clinician weighs when reading your SHBG and testosterone results side by side.
Why One Result May Not Be Enough
Even a single “normal” or “abnormal” figure may not be the full story, because testosterone itself moves around more than most men expect. In an observational study of 87 healthy men, the biological variation between repeat morning measurements was 18.7 percent, which means two tests drawn on different mornings can genuinely differ in the same healthy person.[7]
That natural swing is a big reason many clinicians ask for a second, confirmatory test before settling on any conclusion. Getting the timing right also helps, which is why we wrote a separate guide on testosterone testing timing.
What Should You Ask Your Clinician?
If a testosterone result has left you confused, or your symptoms have stuck around despite a “normal” number, there are a few fair questions worth raising at your next appointment.
You might ask whether the test was done in the morning, since timing affects the reading. You can ask whether SHBG was measured alongside your total testosterone, and whether a free or calculated free testosterone test would add anything useful in your situation. It is also reasonable to ask whether something else, such as thyroid function, iron levels, sleep, or mood, could be feeding your symptoms.
Rest assured that a clinician who works in hormone health can read your results within the full context of your life rather than in isolation. A single value, whether it is total testosterone, SHBG, or free testosterone, is a starting point and not a verdict.
Conclusion
SHBG quietly decides how much of your testosterone is actually available to do its work, which is why a “normal” total can still sit alongside real symptoms. What’s more, age, body weight, thyroid function, and liver health can all shift your SHBG, so the same number can mean different things in different men. The most useful step you can take is an informed conversation with your own clinician, where your symptoms and your full results are read together.
References
- [1] Keevil BG, Adaway J. J Steroid Biochem Mol Biol. 2019, PMID 30970279
- [2] Bhasin S et al., J Clin Endocrinol Metab. 2018, PMID 29562364
- [3] Kaufman JM. Rev Endocr Metab Disord. 2022, PMID 36355322
- [4] Gyawali P et al., PLoS One. 2018, PMID 29995902
- [5] Dumoulin SC et al., Eur J Endocrinol. 1995, PMID 7749500
- [6] Szybiak-Skora W et al., Biomedicines. 2025, PMID 40427034
- [7] Collier CP et al., J Urol. 2010, PMID 20400148
Medically reviewed by Ahmed Zayed, MBBCh, a clinician with 12 years of practice. This article is for education and does not replace a consultation with your own doctor.
