Free testosterone and SHBG: what your blood values really mean

Your total testosterone is perfectly "normal", but you feel far from in top shape. How is that possible? The answer rarely sits in that single total number and almost always in two values your doctor sometimes skips: your free testosterone and your SHBG. Those two decide how much hormone your body can actually use.

My point: fixating on your total testosterone is the most common mistake when reading a hormone result.

What is the difference between total and free testosterone?

Total testosterone is the sum of all the testosterone in your blood: the bound part and the free part. Free testosterone is the small fraction, roughly 1 to 3 percent, that is unbound and that your body can use directly. In addition, a part is loosely bound to albumin and also reasonably available.

It comes down to this: your tissues do not feel your total, but mainly your free and loosely bound testosterone. That is why someone with a perfectly fine total testosterone can still have complaints.

What does SHBG do to your testosterone?

SHBG, in full sex hormone binding globulin, is the protein that binds testosterone tightly. The more SHBG, the less testosterone is freely available. A high SHBG can therefore make a normal total testosterone work out low for your body.

SHBG moves with your health. The table below shows what a high or low SHBG often means, and what it does to your available testosterone.

That is why SHBG is not a side issue, but the key to understanding your total and free testosterone.

Which values do you measure together?

For a usable picture you measure total testosterone, free testosterone and SHBG at once. Many labs calculate free testosterone from your total, SHBG and albumin. With those three together you see not only how much testosterone you have, but also how much of it is available. The General Hormones panel delivers these values in one draw.

The Endocrine Society specifically advises assessing the free fraction in a borderline case, where your total is just normal but you still have complaints. The Dutch College of General Practitioners (NHG) stresses that you always read a deviating result in the context of your complaints.

Calculated or directly measured free testosterone?

There are two ways to determine free testosterone. Most labs calculate it from your total testosterone, SHBG and albumin. That is reliable and affordable, and for most men more than sufficient. There is also a direct measurement, but that method is technically harder and not always more accurate.

For practice it matters little to you: if you measure total, SHBG and albumin together, you have all the ingredients for a good calculation. More important than the method is that you read the three values in context, not separately.

What changes your SHBG in practice?

SHBG is not a fixed given. Your lifestyle and health adjust it. A few concrete examples for active men:

• Losing weight: with excess weight your SHBG is often low. Losing weight can move it towards normal.
• Insulin resistance: a high insulin level coincides with a low SHBG. Your metabolic health counts here too.
• Thyroid: a fast thyroid raises your SHBG, a slow one lowers it.
• Age: SHBG rises gradually over the years, so your free fraction can drop even though your total stays the same.

That actually makes SHBG a handy health gauge in itself. An unexpectedly low SHBG can be an early hint that your metabolic health deserves attention.

What do you do with these values?

If you see a normal total with a high SHBG and complaints, your free fraction may be the explanation. Do not jump to conclusions, but take the three values together and discuss them with your doctor. The complete picture is in the guide testosterone: symptoms and blood values, and how to read your numbers in understanding your testosterone levels.

Can you influence your SHBG yourself?

Partly, yes. Because SHBG moves with your metabolic health, the same things that are good for the rest of your body help here too. Losing weight when overweight, improving your insulin sensitivity with resistance training and curbing your sugar intake can gradually move a low SHBG towards normal.

At the same time, a deviating SHBG is not always a problem you have to solve. Sometimes it is simply a property of your body or your age. The value only gains meaning when you read it together with your total and free testosterone and with your complaints. That is why my advice is: do not chase an SHBG number on its own, but use it to sharpen your testosterone picture. To get that picture in one draw, the General Hormones panel combines the right values.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and cannot replace medical advice. Discuss a deviating result with your GP.

If you have total testosterone, SHBG and albumin on paper, the free testosterone calculator works out the free fraction for you.