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Reproductive Health

SHBG (Sex Hormone Binding Globulin)

SHBG is a protein, made by your liver, that carries your sex hormones — mainly testosterone — through the blood and controls how much is free and active. A high SHBG leaves less testosterone available to your body; a low SHBG leaves more. It is read alongside your testosterone, not on its own, so the number only makes sense with the rest of your hormone picture.

Targeted Testing
CategoryReproductive Health
Reference rangeSee your report
Evidence○Targeted Testing
Last updated3 July 2026
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What is shbg (sex hormone binding globulin)?

Sex hormone binding globulin (SHBG) is a protein produced by the liver. Its job is to bind tightly to sex hormones — mainly testosterone, but also dihydrotestosterone (DHT) and oestradiol (the main female sex hormone) — and carry them through the bloodstream in an inactive form. Only the hormones that are not bound to SHBG (about 2% of the total, called free testosterone) are immediately available for the body's tissues to use. Because SHBG acts as a gatekeeper — controlling how much hormone is free and active — your SHBG level directly shapes the effect your sex hormones have, even if the total hormone level looks normal.

Why is it tested?

An SHBG test is primarily ordered to help assess androgen (male hormone) status. In men, it is used to look for testosterone deficiency; in women, it is used to investigate excess testosterone production. Knowing SHBG is valuable because total testosterone alone can be misleading. Someone with high total testosterone but very high SHBG may actually have little free, biologically active hormone. Conversely, someone with low SHBG may have more free hormone available than their total testosterone suggests. Your GP usually orders SHBG together with total and free testosterone rather than on its own.

Reference range (Australia)

Use the reference interval printed on your report — SHBG is interpreted alongside testosterone rather than as a stand-alone number, and it shifts with age, thyroid and liver status nmol/L

SHBG is read together with testosterone (it sets how much is free/active); it rises with ageing and falls in some conditions, so the report's interval is the comparison.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

A low SHBG means more of your sex hormones are free and active. This is associated with conditions where insulin resistance (the body's reduced response to insulin) plays a role, such as type 2 diabetes or metabolic syndrome. Your GP will consider your SHBG alongside your testosterone and other markers rather than acting on SHBG alone.

If your level is in range

A SHBG result within the reference interval on your report suggests the balance of bound and free hormone is within the expected range for your age and sex. Your GP will read it in context of your other hormone levels and symptoms.

If your level is high

A high SHBG means more of your sex hormones are being bound and held inactive, leaving less free testosterone (or oestradiol) for your tissues to use. This can occur with ageing — SHBG rises significantly as we get older, which is part of why free testosterone falls with age. Oestrogen and oestrogen-containing treatments also stimulate the liver to make more SHBG, increasing binding and reducing the free hormone available. Your GP will read your SHBG together with your total and free testosterone results to understand the full picture.

What can affect your result

Several things move SHBG, which is why it is read with the full hormone picture. Ageing is one of the biggest drivers: SHBG rises significantly as men get older, and this causes a decline in free testosterone — so an older man with a normal total testosterone may still have less active hormone than expected. Oestrogens — both naturally produced and from oral contraceptives or hormone replacement therapy — stimulate the liver to make more SHBG. This increases binding of testosterone and reduces the free, active fraction available. Thyroid function also matters: an overactive thyroid (hyperthyroidism) tends to raise SHBG, while an underactive thyroid (hypothyroidism) can lower it. Liver health affects SHBG production directly, since the liver makes it. Insulin resistance and high insulin levels are associated with lower SHBG, which is one reason SHBG is sometimes checked in people being assessed for polycystic ovary syndrome (PCOS) or metabolic conditions.

When to act

SHBG is most useful as part of a wider hormone panel, not as a single result to act on. If your SHBG is outside the reference interval, your GP will look at it alongside your testosterone, symptoms, and other relevant results — thyroid function, liver markers, and insulin sensitivity — before drawing any conclusions. A result worth discussing at your next GP visit; rarely something that needs urgent attention on its own. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

SHBG is a liver protein that binds tightly to sex hormones — especially testosterone — and carries them in an inactive form in the blood. Only the tiny unbound fraction (roughly 2% of testosterone) is immediately available to your tissues. Because SHBG determines how much is free and active, it directly affects whether you feel the full effect of your hormones, even if your total hormone level looks normal on paper.

Total testosterone tells you how much is in the blood overall, but a lot of it may be bound to SHBG and therefore inactive. SHBG levels tell your GP how much of that testosterone is actually free and available. In men, SHBG is primarily ordered to assess for testosterone deficiency; in women, it helps investigate whether testosterone is present in excess. Reading both together gives a much more useful picture than either alone.

SHBG rises significantly with ageing, which is a key reason free testosterone falls in older men. Oestrogens — whether naturally produced, or from oral contraceptives or hormone replacement therapy — stimulate the liver to produce more SHBG, increasing the binding of testosterone and reducing the free fraction. An overactive thyroid (hyperthyroidism) also raises SHBG.

A high SHBG binds up more of your testosterone, leaving less of it free and biologically active. This means the effect of your testosterone on your body is reduced, even if the total amount measured in the blood looks adequate. As SHBG rises with age, free testosterone declines — this is a well-recognised part of the hormonal shift that comes with growing older, rather than necessarily a disease state.

No — SHBG is most useful as part of an androgen assessment, not as a standalone result. Your GP uses it to understand how much testosterone is free and active, not as a number to act on by itself. A result outside the reference interval is a prompt to look at the whole picture: total testosterone, free testosterone, symptoms, and other relevant markers.

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