SHBG in men: what a high or low value can mean

SHBG (sex hormone-binding globulin) is a protein that binds testosterone in your blood and so sets how much stays free and active. Because of this, your total testosterone can look normal while you still have too little working testosterone, or the other way round. A high SHBG can cause symptoms despite a tidy number, and a low SHBG is often a signal from your metabolism.

I think SHBG is one of the most underrated values on a hormone test. Without SHBG you really only read your testosterone halfway.

What is SHBG?

SHBG is a transport protein made by your liver. It binds testosterone and oestradiol, which keeps those hormones temporarily inactive. Only the free and loosely bound part reaches your tissues (Selby, 1990).

Think of SHBG as a sponge for testosterone. The more sponge, the less floats free to do its work.

What is a normal SHBG value?

In adult men SHBG sits broadly between about 18 and 54 nmol/L, though the reference range varies by lab and rises gradually with age. The value on its own says little: what matters is its ratio to your total and free testosterone.

What does a high SHBG mean?

A high SHBG binds more testosterone, so less free testosterone is left. Your total testosterone can then look normal while you still have symptoms. Common causes are ageing, an overactive thyroid and liver disease (Xita and Tsatsoulis, 2010).

That is why with a high SHBG your free testosterone matters most, not the total alone.

What does a low SHBG mean?

A low SHBG leaves more free testosterone, but is often a signal from your metabolism. It goes with excess weight, insulin resistance, fatty liver and sometimes an underactive thyroid. In that sense a low SHBG is less a hormone problem and more a metabolic signpost.

Reliable Dutch-language patient information on lifestyle and insulin resistance is maintained by GPs at Thuisarts.nl.

Which symptoms fit a high SHBG?

A high SHBG causes no symptoms itself, but its effect does: because less free testosterone is left, you can notice what goes with a low testosterone. Think of less energy, lower libido, less muscle strength or a low mood, while your total testosterone looks fine on paper.

That is exactly the trap. A doctor who looks only at total testosterone can miss the real story when SHBG is high.

Picture a lean man of 60 with a normal total testosterone and yet symptoms. His SHBG turns out high, and his calculated free testosterone low. Only then does the picture fall into place.

A low SHBG rarely causes direct symptoms, but more often points to your metabolism. That is why it pays to place a fasting glucose or HbA1c next to it. In short, with a high SHBG what matters most is what stays free.

What can influence your SHBG?

What can influence your SHBG is mostly tied to your metabolism and your liver. Research links a low SHBG to excess weight and insulin resistance, and a high SHBG to ageing and thyroid activity. That does not mean you should chase a number yourself: what makes sense depends on the cause and on your whole picture. Discuss that with your GP.

How do you read SHBG next to your testosterone?

SHBG only gains meaning next to your total and free testosterone. Labs often calculate free testosterone from those two, because that fraction is the part that reaches your tissues (Narinx et al., 2022). To measure the whole set, the testosterone panel covers testosterone and SHBG, and you also find the separate SHBG value on broader hormone panels. If you want to measure this protein on its own, the standalone SHBG test does that, and the free testosterone test works out the active fraction for you.

So never read SHBG on its own. How LH and FSH fit the picture is in our piece on LH and FSH in men, and the full explanation of your testosterone is in understanding your testosterone levels. For the overview, see male sex hormones. If you see an abnormal value, discuss it with your GP.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

Sources

• Selby C. Sex hormone binding globulin: origin, function and clinical significance. Ann Clin Biochem. 1990. PMID 2080856.
• Xita N, Tsatsoulis A. Genetic variants of sex hormone-binding globulin and their biological consequences. Mol Cell Endocrinol. 2010. PMID 19733622.
• Narinx N, et al. Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone. Cell Mol Life Sci. 2022. PMID 36205798.