What Is SHBG and Why Does It Affect Your Results?

The Short Answer

SHBG (sex hormone-binding globulin) is a protein made mainly by the liver that binds to testosterone (and other sex hormones) in the blood, making them biologically inactive while bound. How much SHBG you have directly affects how much testosterone is “free” and available for your body to use, which is why SHBG is often tested alongside total testosterone rather than on its own.

What SHBG Does

Once testosterone is released into the bloodstream, most of it doesn’t circulate in an active, usable form. Instead, the majority binds to SHBG, with a smaller amount loosely bound to albumin, and only a small fraction (typically 1–2%) remaining completely free and biologically active.

SHBG essentially acts as a carrier and a reservoir, testosterone bound to it is transported through the blood but isn’t available to act on tissues until it’s released. This means SHBG levels have a direct influence on how much active testosterone your body has available at any given time, independent of your total testosterone number.

Why SHBG Matters for Interpreting Your Results

Because SHBG determines how much testosterone is bound versus free, two people can have the same total testosterone level but very different amounts of biologically active testosterone, depending on their SHBG:

High SHBG binds up more testosterone, potentially leaving less free testosterone available, which can result in symptoms of low testosterone even when the total testosterone reading looks normal.
Low SHBG means a larger proportion of total testosterone is free, which can occasionally mean someone with a borderline total testosterone reading still has an adequate amount of active hormone.

This is a key reason why SHBG is included in most comprehensive hormone panels rather than tested in isolation — see total vs. free testosterone for the fuller picture of how these markers interact.

What Raises or Lowers SHBG?

SHBG levels are influenced by a range of factors, including:

Tends to raise SHBG:

Increasing age
Liver disease
Hyperthyroidism (overactive thyroid)
Certain medications, including some anti-epileptic drugs and oestrogen-containing treatments

Tends to lower SHBG:

Obesity and insulin resistance
Hypothyroidism (underactive thyroid)
Use of anabolic steroids
Growth hormone excess

Because SHBG can shift for reasons unrelated to testosterone production itself, an unusual SHBG reading is often a prompt for further investigation into these underlying factors, rather than something to interpret in isolation.

How SHBG Is Used to Calculate Free Testosterone

Direct measurement of free testosterone is technically complex and not always standardised between labs. Because of this, many providers instead calculate a free testosterone estimate (or a related figure called the free androgen index) using total testosterone and SHBG together, sometimes alongside albumin. This calculated approach is widely used in clinical practice and considered a reliable estimate for most purposes.

Should You Get SHBG Tested?

If you’re only curious about a baseline testosterone reading with no symptoms, a single-marker total testosterone test may be sufficient. But if you have symptoms of low testosterone, or your total testosterone comes back in the borderline “grey zone,” testing SHBG alongside it gives considerably more useful information, potentially explaining a normal-looking total testosterone reading that still comes with symptoms. See our comparison of testosterone tests with a full hormone panel that include SHBG as standard.

Frequently Asked Questions

Is high SHBG bad?

Not inherently, SHBG serves an important regulatory role. But unusually high SHBG can lower the amount of free, active testosterone available, which may contribute to symptoms even when total testosterone looks normal.

Does SHBG increase with age?

Yes, SHBG tends to rise gradually with age, which is part of why free testosterone can decline somewhat faster than total testosterone as men get older.

Can lifestyle changes affect SHBG?

Factors like weight, thyroid health, and liver health can all influence SHBG, so addressing underlying issues in these areas may indirectly affect SHBG levels over time. This should be discussed with a GP rather than self-managed based on a single reading.

Is SHBG included in a standard testosterone test?

Not always, many basic single-marker tests measure total testosterone only. SHBG is typically included in fuller hormone panels, which is worth checking for before purchasing if you want a more complete picture.

What’s a normal SHBG level?

Reference ranges vary by lab, and SHBG should generally be interpreted alongside total testosterone and clinical symptoms by a qualified professional, rather than assessed against a generic range alone.